基于Geant4的α粒子能谱模拟研究及软件设计实现

为进一步发展基于蒙特卡罗模拟方法的α粒子能谱探测参数优化技术,利用PyQt5设计一款调用蒙特卡罗模拟程序包Geant4进行α粒子能谱模拟研究的软件。一方面,建立了测量α粒子的钝化离子注入平面硅探测器（Passivated Implanted Planar Silicon）物理模型,根据实际α粒子测量条件对模拟的物理过程、模型材料及粒子源几何形状、成分等参数进行校正,结合PyQt5界面开发平台将粒子源参数、探测器参数修改等功能可视化。在多个探源距和不同真空压强条件下进行模拟实验,得到该模型的探测效率,并将获取的能量沉积成谱后,通过EMG-Landau响应函数模型展宽。另一方面,为验证该探测器模型的准确性,将模拟结果与实测结果的探测效率进行对比,实验结果表明,两者探测效率误差均在5%之内,且EMG-Landau响应函数模型展宽效果良好。本文研究结果验证了该Geant4模拟软件在α粒子能谱研究方面的可靠性,该软件可直观修改α粒子能谱测量条件,简化了模拟步骤,提高了模拟效率,为基于蒙特卡罗模拟方法的α粒子能谱探测参数优化技术提供了有力工具。     

2 1/2维等离子体粒子模拟分布式并行程序设计

设计了两种粒子模拟的并行算法，并对其进行了比较，基于消息传递环境开发2 1/2维粒子模拟并行程序，测试并分析了并行性能。粒子模拟算法中，给出了一个初始化粒子三维Maxwell速度分布的算法，并对常用的电磁场的Lindman吸收边界作了推广。最后对激光钻孔问题作了粒子模拟计算，验证了该并行程序。     

完全匹配层吸收边界在2D3V等离子体粒子模拟中的实现

基于Berenger完全匹配层的基本思想,导出了高斯单位制下2维完全匹配层吸收介质的控制方程及参数设置方法,并进行了数值验证和参数优化。依据所得结论编制了相应的吸收边界模块加入到2D3V等离子体粒子模拟程序PLASIM中,取得了良好的吸收效果。基于完全匹配层吸收边界的实现,在小窗口内对超强激光预脉冲与低密度等离子体的长时间相互作用过程进行了模拟研究,结果表明:激光强度和作用时间是影响等离子体密度改变的重要因素,超强激光其长时间的预脉冲可以通过有质动力的累积效应在低密度等离子体中引起较大的密度变化。     

粒子群及遗传算法在相对论返波管中的应用(英文)

在全三维粒子模拟软件CHIPIC平台上,分别开发了粒子群及基因算法模块.以相对论返波管为例,采用三种不同类型的参数(连续参数、离散参数、混合参数),对粒子群及基因算法进行比较.优化结果表明:粒子群算法的收敛速度更快,在有限的迭代步数内得到的目标结果也更优良,总体表现优于基因算法.     

高功率微波器件2.5维通用粒子模拟软件——尤普

 利用体积加权宏粒子模型,考虑了阴极形状的爆炸电子发射模型、散度校正完全匹配层边界等新型和改进型电磁粒子模拟算法模型,提高了粒子模拟算法的计算精度,并有效降低数值噪声。在此基础上开发出2.5维全电磁通用粒子模拟软件——尤普,可在x-y,z-r和r-φ3种坐标系下应用于高功率微波器件的2.5维数值模拟研究和结构设计。对相对论磁控管、磁绝缘线振荡器和虚阴极振荡器等高功率微波器件的模拟结果表明：尤普软件得到了正确的物理图像和物理规律。     

基于粒子模拟和并行遗传算法的高功率微波源优化设计

提出了基于粒子模拟和并行遗传算法的高功率微波源优化设计方法, 以全电磁粒子模拟软件UNIPIC模拟的高功率微波器件输出功率作为适应度函数, 采用浮点数编码的遗传算法对高功率微波源器件进行优化. 采用该算法, 对相对论返波管的布拉格反射器位置以及高度进行了浮点数编码,然后在巨型机上进行参数的全局优化, 获得了该返波管布拉格反射器的全局最优参数. 关键词： 并行遗传算法 相对论返波管 粒子模拟 高功率微波源     

爆炸电子发射边界的粒子模拟实现

 介绍了自行研制的全电磁柱坐标粒子模拟程序的电流分配方法和金属爆炸电子发射边界的模拟实现，该电流分配方法满足电荷电流连续性方程，避免了繁琐的泊松修正，适用于复杂边界物理问题的模拟研究。基于此电流分配方法的基础上，给出了建立在高斯定理基础上的简单且易于程序实现的阴极发射边界算法。利用该程序对平面二极管电子发射现象的模拟结果证明了算法的正确性。     

爆炸复合边界效应的数值模拟

借助动力学分析软件ANSYS/LS-DYNA,运用光滑粒子流体动力学(SPH)方法,对爆炸复合边界效应进行了二维数值模拟。模拟结果再现了爆炸复合过程中的射流现象和边界效应。研究结果表明,爆炸复合边界效应的产生原因并非是边界处的冲击能量过剩,在基-复板碰撞之前,断裂就已经产生。采用SPH方法对爆炸复合边界效应进行模拟研究具有一定的科学价值。     

全三维55GHz双阳极磁控注入式电子枪数值模拟

根据绝热压缩和角动量守恒理论对55GHz双阳极磁控式注入枪进行了初始参数的设计,并利用自主研发的三维粒子模拟软件CHIPIC对其进行数值模拟,通过改变阴极半径、电子注电流、阴极磁场等参数来分析其对磁控注入式电子枪输出结果的影响。最终通过优化参数和综合因素的考虑,得到了横纵速度比为1.44、最大速度零散为5.8%的高性能电子束,能够很好满足55GHz回旋振荡管对电子束的要求。     

光学薄膜椭圆偏振数据反演的优化算法

运用C++语言通过变步长循环的优化算法开发数据处理程序,利用2组数据确定了多周期真实厚度.通过计算SiO2和ZrO薄膜的折射率和单周期及多周期厚度,并与其他方法的计算结果进行对比分析,发现此方法计算结果可以达到较高的精度.对于有吸收的薄膜,利用量子力学原理计算粒子出现在某一点的概率,通过蒙特卡罗模拟的方式来测量粒子的位置,从而对粒子进行刷新.通过基于量子行为粒子群优化和模拟退火的混合算法设计的程序进行计算,可很快跳出局部极小收敛达到全局最优点,在保证精度的同时达到较快的收敛速度.     

基于Z变换的高阶完全匹配层实现(英文)

基于拉伸坐标完全匹配层(SC-PML)公式和Z变换方法,提出以非分裂场形式来实现具有多极点的高阶完全匹配层的高效算法,来截断时域有限差分(FDTD)网格.在吸收性能方面,高阶PML同时具有传统PML和复频率偏移完全匹配层(CFS-PML)二者的优点.提供的数值算例是二维TE极化电磁波与无限长且有限宽度的理想电导体(PEC)薄片的相互作用.仿真结果显示,高阶PML公式在衰减低频行波和隐失波及减少后期反射方面效果好,比传统SC-PML和复频率偏移的卷积完全匹配层(CPML)算法有更好的吸收性能.     

2.5维圆波导开放边界截断的修正完全匹配层方法

 在时域有限差分算法中，完全匹配层是一种高效的吸收边界条件。通过在标准完全匹配层(PML)方程中添加具有物理意义的电导率和导磁率附加项，提出了修正完全匹配层(MPML)方法，给出了圆柱坐标下3维MPML方程，并应用于2.5维圆波导开放边界的截断计算。计算结果表明，在不同频率和模式的激励下，加入平滑电导率和导磁率附加项后，与标准PML方法相比，MPML方法的相对误差降低8~10 dB。     

The Improvement of PML Approach for the Calculation of Microwave and Millimeter Waves Circuit

The improved PML absorbing boundary condition have been introduced in this paper. The reflection coefficient of the absorbing boundary condition is less than the reflection coefficient of Berenger's PML algorithm. And in order to validate the theory and its effectiveness, We have applied the absorbing boundary condition to the calculation of microwave and millimeter waves circuit and get its reflection coefficient S ₁₁. The numerical result is shown in this paper.     

A novel unsplit perfectly matched layer for the second-order acoustic wave equation

When solving acoustic field equations by using numerical approximation technique, absorbing boundary conditions (ABCs) are widely used to truncate the simulation to a finite space. The perfectly matched layer (PML) technique has exhibited excellent absorbing efficiency as an ABC for the acoustic wave equation formulated as a first-order system. However, as the PML was originally designed for the first-order equation system, it cannot be applied to the second-order equation system directly. In this article, we aim to extend the unsplit PML to the second-order equation system. We developed an efficient unsplit implementation of PML for the second-order acoustic wave equation based on an auxiliary-differential-equation (ADE) scheme. The proposed method can benefit to the use of PML in simulations based on second-order equations. Compared with the existing PMLs, it has simpler implementation and requires less extra storage. Numerical results from finite-difference time-domain models are provided to illustrate the validity of the approach.     

Frequency domain finite-element and spectral-element acoustic wave modeling using absorbing boundaries and perfectly matched layer

Wave propagation modeling as a vital tool in seismology can be done via several different numerical methods among them are finite-difference, finite-element, and spectral-element methods (FDM, FEM and SEM). Some advanced applications in seismic exploration benefit the frequency domain modeling. Regarding flexibility in complex geological models and dealing with the free surface boundary condition, we studied the frequency domain acoustic wave equation using FEM and SEM. The results demonstrated that the frequency domain FEM and SEM have a good accuracy and numerical efficiency with the second order interpolation polynomials. Furthermore, we developed the second order Clayton and Engquist absorbing boundary condition (CE-ABC2) and compared it with the perfectly matched layer (PML) for the frequency domain FEM and SEM. In spite of PML method, CE-ABC2 does not add any additional computational cost to the modeling except assembling boundary matrices. As a result, considering CE-ABC2 is more efficient than PML for the frequency domain acoustic wave propagation modeling especially when computational cost is high and high-level absorbing performance is unnecessary.     

Unconditionally Stable Complex Envelope Wave Equation PML Algorithm for Band Limited FDTD Simulations

Unconditionally stable complex envelope (CE) perfectly matched layer (PML) absorbing boundary conditions (ABCs) are presented for truncating the scalar wave-equation finite difference time domain (WE-FDTD) grids. The formulations are based on incorporating the alternating direction implicit (ADI) scheme into the CE FDTD implementations of the scalar wave-equation derived in the PML region at the domain boundaries. Numerical example carried out in two dimensional domain shows that the proposed formulations are more accurate than the classical ADI scalar wave equation PML formulations when it is used for modelling band limited electromagnetic applications.     

基于辅助差分方程的完全匹配层在时域多分辨率分析算法中的应用与性能分析

将基于辅助微分方程的完全匹配层(ADE-PML)吸收边界条件引入到基于Daubechies尺度函数的时域多分辨率分析算法中. 与目前广泛应用的Berenger完全匹配层(PML)和各向异性介质完全匹配层(APML) 相比, 该吸收边界条件的实现更加容易且更节省内存. 数值结果表明, ADE-PML在吸收传播模和低频凋落模方面均优于PML和APML.     

Absorbing boundary conditions for nonlinear Euler and Navier–Stokes equations based on the perfectly matched layer technique

Absorbing boundary conditions for the nonlinear Euler and Navier–Stokes equations in three space dimensions are presented based on the perfectly matched layer (PML) technique. The derivation of equations follows a three-step method recently developed for the PML of linearized Euler equations. To increase the efficiency of the PML, a pseudo mean flow is introduced in the formulation of absorption equations. The proposed PML equations will absorb exponentially the difference between the nonlinear fluctuation and the prescribed pseudo mean flow. With the nonlinearity in flux vectors, the proposed nonlinear absorbing equations are not formally perfectly matched to the governing equations as their linear counter-parts are. However, numerical examples show satisfactory results. Furthermore, the nonlinear PML reduces automatically to the linear PML upon linearization about the pseudo mean flow. The validity and efficiency of proposed equations as absorbing boundary conditions for nonlinear Euler and Navier–Stokes equations are demonstrated by numerical examples.     

有耗介质空间完全匹配层吸收边界条件及其应用

 针对Gedney提出的完全匹配层(PML)无法用于有耗各向同性计算域的截断及其对倏逝波的衰减不理想等问题,提出了一种扩展方法。扩展的PML的主要思想是在各向异性的PML中引入与有耗介质空间相一致的复介电常数和复磁导率,使之可以与有耗介质计算域相匹配。通过给PML的张量介电常数、张量磁导率增加衰减因子以加速倏逝波的衰减。构造了PML吸收效果验证模型,数值结果证明了扩展的PML在处理有耗介质计算域截断问题中的有效性。利用该吸收边界条件,采用时域有限差分法计算了电磁脉冲作用下地面铺设电缆的电磁脉冲响应,计算结果和试验结果取得了较好的一致。