Static and free vibration analyses of functionally graded porous variable-thickness plates using an edge-based smoothed finite element method

The main purpose of this paper is to present numerical results of static bending and free vibration of functionally graded porous (FGP) variable-thickness plates by using an edge-based smoothed finite element method (ES-FEM) associate with the mixed interpolation of tensorial components technique for the three-node triangular element (MITC3), so-called ES-MITC3. This ES-MITC3 element is performed to eliminate the shear locking problem and to enhance the accuracy of the existing MITC3 element. In the ES-MITC3 element, the stiffness matrices are obtained by using the strain smoothing technique over the smoothing domains formed by two adjacent MITC3 triangular elements sharing an edge. Materials of the plate are FGP with a power-law index (k) and maximum porosity distributions (Ω) in the forms of cosine functions. The influences of some geometric parameters, material properties on static bending, and natural frequency of the FGP variable-thickness plates are examined in detail.     

Formation and characterization of core-shell CL-20/TNT composite prepared by spray-drying technique

The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene (CL-20/TNT) composite was prepared by spray-drying method in which sensitive high energy explosive (CL-20) was coated with insensitive explosive (TNT). The structure and properties of different formulations of CL-20/TNT composite and CL-20/TNT mixture were characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Laser particle size analyzer, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impact sensitivity test and detonation performance. The results of SEM, TEM, XPS and XRD show that ϵ-CL-20 particles are coated by TNT. When the ratio of CL-20/TNT is 75/25, core-shell structure is well formed, and thickness of the shell is about 20–30 nm. And the analysis of heat and impact show that with the increase of TNT content, the TNT coating on the core-shell composite material can not only catalyze the thermal decomposition of core material (CL-20), but also greatly reduce the impact sensitivity. Compared with the CL-20/TNT mixture (75/25) at the same ratio, the characteristic drop height of core-shell CL-20/TNT composite (75/25) increased by 47.6% and the TNT coating can accelerate the nuclear decomposition in the CL-20/TNT composites. Therefore, the preparation of the core-shell composites can be regarded as a unique means, by which the composites are characterized by controllable decomposition rate, high energy and excellent mechanical sensitivity and could be applied to propellants and other fields.     

Recursive weighted least squares estimation algorithm based on minimum model error principle

Kalman filter is commonly used in data filtering and parameters estimation of nonlinear system,such as projectile's trajectory estimation and control.While there is a drawback that the prior error covariance matrix and filter parameters are difficult to be determined,which may result in filtering divergence.As to the problem that the accuracy of state estimation for nonlinear ballistic model strongly depends on its mathematical model,we improve the weighted least squares method(WLSM)with minimum model error principle.Invariant embedding method is adopted to solve the cost function including the model error.With the knowledge of measurement data and measurement error covariance matrix,we use gradient descent algorithm to determine the weighting matrix of model error.The uncertainty and linearization error of model are recursively estimated by the proposed method,thus achieving an online filtering estimation of the observations.Simulation results indicate that the proposed recursive esti-mation algorithm is insensitive to initial conditions and of good robustness.     

Polarization visualization for low-irradiance regions by perceptually uniform color space

Currently,polarization visualization strategies are accomplished by mapping polarization information into a perceptually uniform color appearance model CAM02-UCS.However,the deviation of the CAM02-UCS space from the lightness prediction results in an inaccurate match between the polarization in-formation and the perceptual information.In this paper,we propose a novel polarization visualization strategy based on the perceptual uniform space Jzazbz.The polarization visualization be completed by placing the polarization information into the lightness Jz,colorfulness Cz and hue angle hz channels of the Jzazbz space.The experimental results show that the proposed method can significantly improve the lightness of the low irradiance and high polarization region,hence more polarization information can be sensed by human visual system.     

基于随机有限集理论的多传感器目标联合检测跟踪算法

针对杂波环境中的目标检测跟踪问题,提出一种基于随机有限集理论的多传感器目标联合检测跟踪算法。算法将目标状态和量测描述为随机集合,建立考虑目标出现、目标保持、目标消失等情况的目标状态随机有限集模型,以及考虑漏检和虚警的多传感器量测随机有限集模型。将目标的联合检测跟踪问题构建为目标状态集合的贝叶斯最优估计问题,并基于随机有限集理论对该贝叶斯估计算法的递推表达式进行严格理论推导。采用序贯蒙特卡罗技术实现算法的递推滤波。仿真结果验证了该算法的有效性以及算法相对于传统基于数据关联算法的性能优势。     

听力教学中“环境训练法”的实验研究

本文就学生在听力技能训练中普遍存在较为突出的问题:大脑疲劳与精神紧张,从心理学和生理学的角度提出了"环境训练法".其目的是通过放松练习来改善大脑环境从而使学生在轻松愉快的状态下积极高效地练习听力.通过实验对比与分析,实验组与对照组相比p<0.01,实验组听力成绩明显优于对照组.实验研究证明这一方法具有实用性与有效性.     

非定常超音速流动数值计算方法比较

为适用于非定常流场计算 ,在保证时、空二阶精度的前提下 ,通过引入变系数残值光顺技术 ,提高了四步Runge Kutta方法的计算效率 ;并针对球锥简谐振动过程 ,数值比较Runge Kutta多步法和“双时间法”的计算精度。     

基于面元法的航母雷达散射截面计算

采用 3DStudioMAX对航母进行三角面元逼近模拟 ,并用面元法研究计算了航母在X波段的雷达反射特性 ,给出了航母雷达散射截面 (RCS)随方位的分布图。从图中可以看出 ,航母的RCS峰值出现在船头、船尾和两舷四个方向 ,这说明航母的雷达回波主要来自于镜面反射。     

改善机载前向阵雷达全程检测性能的研究

针对前向阵的杂波分布特性 ,给出了一种空时自适应处理 (STAP)结合多重中脉冲重复频率(MPRF)的处理方案 ,研究了重复频率的选择以改进系统性能 ,并分析计算了三路多普勒通道联合处理STAP方法在一组中脉冲重复频率下的改善因子和距离 /速度二维盲区分布图。理论分析与仿真结果表明 ,该方案可以大大改善机载前向阵雷达的全程检测性能     

混沌控制: 回顾与展望

回顾了混沌控制产生的背景 ,重点介绍了OGY方法的思想、原理和特点 ,简要概括了十年来的一些重要进展 ,并对今后的发展方向和可能存在的困难提出了一些见解。