AES轮变换的代数正规型及其应用

每个布尔函数的代数正规型(ANF)是唯一的,对于研究布尔函数有重要意义.利用Mathematica软件得到了高级加密标准的轮变换(Sbox,ShiftRow和MixColumn的复合)的128个分量函数的代数正规型.每个分量函数都是32元布尔函数,其项数在448 ～ 545,平均为496,远远小于随机32元布尔函数的平均项数231.这表明AES轮变换与随机置换有巨大偏差.得到这些ANF的时间复杂度在一个2GHz的PC机上只用几分钟.该方法优于通过真值表得到ANF的经典算法——其得到128个分量函数的时间复杂度为0( 128×32 ×232)=0(244).作为应用,利用得到的ANF建立了一轮AES的一个方程系统,并用Cryptominisat 2.9.0进行求解.使用Guess-and-Determine的方法,利用一个已知明密对,可以在PC机上233h内得到全部128比特密钥.     

Effect of the end cap on the fragment velocity distribution of a cylindrical cased charge

The prediction of the fragment velocity distribution of a cylindrical cased charge with end caps is one of the key issues to assess the damage efficiency of the warhead. However, limited work has been con-ducted to predict the fragment velocity distributions along the axis of cylindrical cased charges with end caps. This paper presents a study of the velocity distribution of fragments caused by the explosion of a cylindrical cased charge with end caps. The fragment velocity distribution and the end cap velocity were determined by an X-ray radiography method, and the axial fragment distribution was determined by witness plates. It was found that the velocities of fragments, especially near the edge, were increased when the end caps were added, and the position of maximum velocity is closer to the non-detonation end. The fragment velocities were increased, and the fragment projection range was decreased with the increase of the thickness of the end cap. A formula for fragment velocity distributions of a cylindrical cased charge with end caps, which is based on Huang's formula, was proposed by the theoretical analysis and data fitting and validated experimentally. The results indicate that the proposed formula is accurate in predicting the fragment velocity distribution along the axis of a cylindrical cased charge with end caps detonated at one end.     

Fragment spatial distribution of prismatic casing under internal explosive loading

Non-cylindrical casings filled with explosives have undergone rapid development in warhead design and explosion control. The fragment spatial distribution of prismatic casings is more complex than that of traditional cylindrical casings. In this study, numerical and experimental investigations into the fragment spatial distribution of a prismatic casing were conducted. A new numerical method, which adds the Lagrangian marker points to the Eulerian grid, was proposed to track the multi-material interfaces and material dynamic fractures. Physical quantity mappings between the Lagrangian marker points and Eulerian grid were achieved by their topological relationship. Thereafter, the fragment spatial distributions of the prismatic casing with different fragment sizes, fragment shapes, and casing geometries were obtained using the numerical method. Moreover, fragment spatial distribution experiments were conducted on the prismatic casing with different fragment sizes and shapes, and the experimental data were compared with the numerical results. The effects of the fragment and casing geometry on the fragment spatial distributions were determined by analyzing the numerical results and experimental data. Finally, a formula including the casing geometry parameters was fitted to predict the fragment spatial distribution of the prismatic casing under internal explosive loading.     

NEPE类推进剂燃烧模拟

在分析、研究硝胺和AP CMDB推进剂燃烧模型的基础上,结合NEPE类推进剂的配方和燃烧性能特点,建立了NEPE类推进剂燃烧的物理模型,并进行了燃速和压强指数的理论计算。结果表明,几乎100%的计算结果都在实验值的±10%范围内。这说明所建立的模型基本合理,编制的NEPE类推进剂燃速计算程序基本可行。     

往返搜索发现概率仿真分析与应用

往返搜索是一种最常见的搜索样式,其搜索效能与搜索宽度、发现距离、搜索速度、突破速度等因素密切相关。在建立往返搜索行动模型的基础上,通过仿真实验得到耕耘数据,进而通过数据分析和处理得到往返搜索发现概率的经验公式。应用经验公式并结合声纳探测模型,对多搜索艇分段封锁搜索案例进行了优化研究。     

雷电回击地面水平电场的解析求解

假定大地为良导电平面 ,基于DU模型计算了雷电回击地面电磁场 ,并探讨了地面水平电场的求解。对于雷电回击水平电场的两种近似求解方法———大地表面阻抗法和斜波法 ,进行了解析推导 ,并从数学上证明了两种方法在远区场的等价法。     

非线性Duffing方程自由振动频率解分析

应用Gauss-Chebyshev求积公式求解了Duffing方程的自由振动频率,得到了高精度近似计算公式。对Duffing方程精确椭圆积分频率解进行了数值计算,以此结果为基准,通过绘制多种典型方法得到的Duf-fing方程自由振动频率解的频率-振幅曲线,定性分析了各公式的精度。以Duffing方程特征振幅为基准,定量分析了各公式的计算值及其相对误差,指出基于Gauss-Chebyshev求积公式的Duffing方程自由振动频率解表达式具有形式简洁、精度高的优点,其优势在大振幅情况下以及软弹簧系统中更为明显。最后指出,现有的频率解在计算精度方面存在一定的差异,有的适合软弹簧系统,有的适合硬弹簧系统,应注意区分它们的适用范围,而应用Gauss-Chebyshev求积公式得到的结果则具有普适性。     

势流理论的一种数值方法在空泡形态中的应用

基于势流理论的假设,采取常规边界元法对具有自由面的定常平板和轴对称空泡流动数值方法进行了研究,运用Riabourichinsky镜像空化模型,建立了一种空泡自由面求解的优化迭代方法,以自由流线长度为参数求解模拟了定常无重工况下流经二维平板和轴对称圆盘的空化流动.数值计算结果与解析解的相对误差不超过3%,证实了轴对称体空泡外形的近似回转椭球体假说在空化器附近是不成立的.计算结果与同类文献数据的对比显示了边界元法进行空化流场计算具有着显著的优越性,所采用的迭代方法精度高、收敛速度快,所得结论对深入了解空化特性具有参考价值.     

用线性兴波阻力理论计算穿浪双体船的兴波阻力

以线性兴波阻力理论 (薄船理论 )Michell型兴波阻力计算公式为基础 ,结合穿浪双体船的船型特点 ,建立了一次和二次简化的Michell型兴波阻力计算公式 ,并以此简化公式计算了某穿浪双体船WPC×××的兴波阻力 .将计算结果与马丁法计算结果进行了比较 ,并探讨了兴波阻力规律及片体间距对WPC兴波阻力的影响规律 .     

决定电视侦察弹射击诸元弹道模型的建立与仿真

在分析电视侦察弹各阶段弹道特点的基础上,建立了求取弹道诸元和射击诸元的弹道数学模型,给出了简单、精确、快速逼近目标的方法,并利用该模型进行了弹道逼近和决定射击诸元的模拟计算.结果表明在初始射角赋予非常简单的条件下,只用两条弹道,再通过一次插值,即可逼近开舱点,获得射击开始(装定)诸元.此模型和方法可用于射表编制和指挥自动化系统.