以捷径法提高射线追踪效率

为改善计算效率,提出了一种捷径法对射线追踪法进行改进. 射线追踪的计算时间主要耗费在求交判断上. 通过实际计算并记录一条射线管的轨迹,作为其后若干条射线管求交计算的优先参考,避免了再次进行漫无目的的遍历式求交,从而大量减少进行实际计算的射线管数量,节省射线求交运算时间. 经编程计算验证,该优化算法能够在保证相当精度的前提下,大幅度提高射线追踪法的计算效率,具备一定的实用价值.      

用射线法研究复杂目标的电磁散射特征

应用计算机图形学中的曲面造型方法给出目标精确的数学外形,将之离散为三角面元,并采用拓扑结构来描述几何元素之间的关系;利用射线追踪法模拟射线束的多次反射,同时求出扩散因子、磁场方向和相位差;在最终反射点处采用物理光学积分求远场散射,叠加每一射线束的贡献,进而得出耦合雷达散射截面值.为减小射线追踪过程中的计算量,采用了加速算法.给出了作为特例的翼身组合体的计算结果.     

邻域辅助径迹法提高射线追踪效率

针对面元形式的目标数据,从提高入射点求解的成功率着手,采用增加对参考路径上参考面元的相邻单元进行相交性判断的方法,并将普通径迹法的单参考路径改为双参考路径,提高了径迹法射线追踪的效率.对邻域辅助径迹法在样条曲面格式目标文件上的应用作了探讨.分析了该方法与其它方法的兼容性和对计算资源的占用情况,给出了该方法提高射线追踪速度的上限.以2个典型目标为例,对该方法的效果进行了测试.结果表明,该方法通过减少真实、遍历式追踪的次数,能将普通径迹法射线追踪过程的计算量减少到原来的1/3左右.该方法对目标具有很强的适应性,并克服了普通径迹法对射线管的划分密度的依赖性.      

非结构重叠网格显式装配算法

针对重叠网格中洞映射法占用过多物理内存的问题,发展了一种改进型洞映射法;基于相邻单元搜索法,发展了一种基于相邻阵面的贡献单元搜索法;通过将割补法与隐式切割技术相结合提出了一种非结构重叠网格显式装配算法。该算法首先生成一套包围物面的笛卡儿网格,其次存储所有与物面边界相交的笛卡儿网格信息,最后根据所存储笛卡儿网格与所需判断的网格单元的相对位置来判断其是否为洞内单元。在成功判断出所有洞内单元后,以当前洞边界为初始阵面推进,同时以各个网格单元的物面距离为判别标准对重叠区域进行优化,生成最终插值边界。所提算法优化了传统非结构重叠网格装配过程,具有物理内存占用低,贡献单元搜索次数少以及计算效率高等特点。通过2个典型复杂流动算例验证了所提算法的准确性与适用性。      

重叠网格中隐式装配策略的改进

作为重叠网格技术的重要组成部分，隐式装配没有显式的“挖洞”过程，仅需在搜索贡献单元的同时通过对比不同单元的品质来分类单元。通过对传统隐式装配过程进行改进，提出了一种更高效的隐式装配策略，减少了贡献单元的搜索次数；同时，提出了一种基于笛卡儿网格映射的局部贡献单元搜索法，提高了网格装配效率。首先，针对每一个子网格，在计算其到自身物面的最短物面距离的同时也计算到其他所有物面的最短物面距离；然后，通过比较同一单元到不同物面的最短物面距离来控制洞边界的位置；最后，仅对插值单元进行局部的贡献单元搜索，避免了针对所有单元进行全局贡献单元搜索的过程。通过3个典型复杂流动算例验证了所提方法的准确性与高效性。      

任意曲面上射线的寻迹方法

为计算任意曲面上天线间的隔离度,提出一种射线寻迹的新算法——最小夹角法.首先对任意曲面表面进行三角形网格剖分,并按照文中要求的格式生成模型表面网格数据;用文中提出的“最小夹角法”对上述网格数据进行处理,从而达到快速准确地找出任意曲面上、任意两点间的短程线.求解了位于圆柱体、椭球体及任意组合体上任意两点间的短程线长度,验证了“最小夹角法”的准确性.     

任意曲面上射线的寻迹方法

为计算任意曲面上天线间的隔离度,提出一种射线寻迹的新算法——最小夹角法.首先对任意曲面表面进行三角形网格剖分,并按照文中要求的格式生成模型表面网格数据;用文中提出的"最小夹角法"对上述网格数据进行处理,从而达到快速准确地找出任意曲面上、任意两点间的短程线.求解了位于圆柱体、椭球体及任意组合体上任意两点间的短程线长度,验证了"最小夹角法"的准确性.     

基于网格细化技术的地球-火星转移轨道优化

文章从细化效率、易用性和适应性等角度对基于数据压缩原理的网格细化算法进行改进,与基于局部配点法开发的通用轨迹优化方法（考虑非线性规划的规范化处理、稀疏特性和数值微分算法）相结合,构建出一种非光滑轨迹优化方法。对地球—火星转移轨道进行了优化,结果表明：所述方法能够高精度、快速求解地球—火星转移轨道优化问题,能够在轨道变化剧烈区域加密网格,在轨道变化平坦区域采用较稀的网格,具有较好的适应性和在线优化的潜力;采用控制变量作为网格细化函数即可捕捉到状态变量的剧烈变化;对于地球—火星转移轨道优化问题,推力方向角定义在[0°,360°)比定义在[-180°,180°)更利于数值优化。     

三维计算流体力学流场的流线构造

流线的计算与显示是流场可视化中的一项基本技术.通过将CFD(Computational Fluid Dynam ics)的计算网格剖分为四面体单元并设置相邻四面体之间的拓扑关系,运用基于四面体侧面 法矢的"指南针"法进行快速点定位,采用自适应步长的数值积分方法直接在物理空间中进 行流线的追踪,避免了物理空间和计算空间之间的转换以及由此所带来的误差,提高了流线 追踪的精度和效率.      

基于DSI插值的三角网格质量优化

通过对三角网格的单元顶点进行几何位置调整,提高了网格的质量,实现了网格的质量优化.几何位置调整是使用离散点光滑插值(DSI,Discrete Smooth Interpolation)实现的,针对在计算时影响质量优化的邻接边界的单元顶点,采用了在边界处补偿三角形的方法,消除了单元收缩,提高了网格的质量.与加权拉普拉斯算法进行了比较和分析,优于拉普拉斯算法;为了使三角网格在位置调整时保持原始网格的几何细节特征,在插值算法中施加了控制点约束.最后使用算例对算法进行了验证.      

机载公共设备综合管理系统任务分配算法研究

机载公共设备的综合管理是机载系统发展的必然方向,为解决机载公共设备综合管理系统中任务分配问题,进行了任务划分.根据周期任务和非周期任务对系统风险系数的贡献不同,提出了两层任务分配策略;以单机风险系数均衡为目标函数,设计了基于蚁群算法的周期任务分配算法.对蚁群算法进行了模糊自适应参数调整的改进,仿真结果表明改进算法能够有效地使蚁群算法从局部最优点中逃脱,解决任务分配问题.      

A study of the ground level enhancement of 23 February 1956

One of the greatest and most famous increase of solar cosmic rays over the neutron monitor epoch is the ground level enhancement in 1956. All future proton events are inevitable when compared with this one and therefore it is necessary to provide the efficiency of such a comparison derived from the existing data. In this paper, we return to the analysis of ground level observations on 23 February 1956 in order to model more precisely the solar cosmic ray behaviour. The extremely high magnitude of this effect allowed various spectral characteristics of solar cosmic rays, their anisotropy, differential and integral proton fluxes, and angular distribution of the source of solar particle anisotropy to be obtained with sufficient accuracy on the basis of available data from 13 neutron monitors. The most outstanding feature of this event was a narrow and extremely intensive beam of ultra relativistic particles arriving at Earth at the beginning of the event. This unique beam was not long and its width did not exceed 30–40°, thus, its contribution to solar particle density was not significant. Many features of this GLE are apparently explained by the peculiarity of particle interplanetary propagation from a remote (limb or behind of limb) source.     

Modeling the solar cosmic ray event of 13 December 2006 using ground level neutron monitor data

In order to understand the physics under extreme solar conditions such as those producing ground level enhancements of solar cosmic rays, it is important to use accurate and reliable models. The NM-BANGLE Model is a new cosmic ray model which couples primary solar cosmic rays at the top of the Earth’s atmosphere with the secondary ones detected at ground level by neutron monitors during GLEs. This model calculates the evolution of several GLE parameters such as the solar cosmic ray spectrum, anisotropy and particle flux distribution, revealing crucial information on the energetic particle propagation and distribution. The total output of the NM-BANGLE Model is a multi-dimensional GLE picture that gives an important contribution to revealing the characteristics of solar energetic particle events recorded at ground level. In this work, the results of the NM-BANGLE Model application to the recent GLE of 13 December 2006 are presented and discussed. Moreover, a comparison with the extreme event of 20 January 2005 (GLE69) has been realized.     

Ion production and ionization effect in the atmosphere during the Bastille day GLE 59 due to high energy SEPs

The influence of high energy particles, specifically cosmic rays, on atmospheric physics and chemistry is highly discussed. In most of the proposed models the role of ionization in the atmosphere due to cosmic rays is not negligible. Moreover, effect(s) on minor constituents and aerosols are recently observed, specifically over the polar regions during strong solar particle events. According to the recent findings for such effects it is necessary an essential increase of ion production, specifically during the winter period. The galactic cosmic rays are the main source of ionization in the Earth’s stratosphere and troposphere. Occasionally, the atmospheric ionization is significantly enhanced during strong solar energetic particles events, specifically over the polar caps. During the solar cycle 23 several strong ground level enhancements were observed. One of the strongest was the Bastille day event occurred on 14 July 2000. Using a full Monte Carlo 3-D model, we compute the atmospheric ionization, considering explicitly the contribution of cosmic rays with galactic and solar origin, focusing on high energy particles. The model is based on atmospheric cascade simulation with the PLANETOCOSMICS code. The ion production rate is computed as a function of the altitude above the sea level. The ion production rate is computed on a step ranging from 10 to 30?min throughout the event, considering explicitly the spectral and angular characteristics of the high energy part of solar protons as well as their time evolution. The corresponding event averaged ionization effect relative to the average due to galactic cosmic rays is computed in lower stratosphere and upper troposphere at various altitudes, namely 20?km, 15?km, 12?km and 8?km above the sea level in a sub-polar and polar regions. The 24^h and the weekly ionization effects are also computed in the troposphere and low stratosphere. Several applications are discussed.     

飞机总体协同优化中的一种混合混沌算法

针对协同优化应用中所碰到的计算困难,分析了现有改进方式。将系统级优化转化成无约束优化问题,选择智能优化算法是一种有效的解决方法,但应注意计算量的控制.将混沌优化和单纯形法相结合,构造出一种混合混沌算法.混沌能有效地跳出局部最优解而接近全局最优点,同时利用单纯形法在混沌优化解的邻域内局部寻优.用协同优化方法对某型干线客机进行总体方案设计;同时各学科级采用序列二次规划法,系统级采用混合算法寻优.计算结果表明此方法是有效的.      

Computation of radiation environment during ground level enhancements 65, 69 and 70 at equatorial region and flight altitudes

The radiation environment in the troposphere of the Earth is governed by cosmic rays of galactic and solar origin. During major solar energetic particles events the radiation environment changes dramatically. As a results the risk of biological effects due to exposure to ionizing radiation of aircrew increases. Here we present a numerical model for computation of absorbed dose in air due to cosmic rays of galactic and solar origin. It is applied for computation of radiation environment at flight altitude in the equatorial region during several major ground level enhancements, namely GLE65 on 28 October 2003, GLE69 on 20 January 2005 and GLE70 on 13 December 2006. The model is based on a full Monte Carlo simulation of cosmic ray induced atmospheric cascade. The cascade simulation is carried out with CORSIKA 6.990 code with corresponding hadron generators FLUKA 2011 and QGSJET II. The contribution of different cascade components, namely electromagnetic, hadron and muon is explicitly obtained. The spectra of arriving solar energetic particles are calculated from ground level measurements with neutron monitors and satellite data from GOES. The obtained results are discussed.     

LET-distributions and doses of HZE radiation components at near-Earth orbits.

Among cosmic rays, the heavy nuclei ranging from carbon to iron provide the principal contribution to the dose equivalent. The LET-distributions and absorbed dose aid dose equivalent have been calculated and are presented as a function of shielding and tissue self-shielding. At solar minimum, outside the magnetosphere, the unshielded dose equivalent of nuclei with atomic number Z > or = 6 is about 47 rem/year. The contribution of the target nuclei adds 7 rem/year. With 4 g/cm2 aluminum shielding, and at a depth of 5 cm in a biological phantom of 30 cm diameter, the respective values are 11 and 10 rem/year. Corresponding dose rates for orbits with various inclinations are presented, as well as the LET distributions of various components of cosmic rays.