基于XFEM和正交实验法的裂纹参数对扭杆强度影响的分析

为研究裂纹对扭杆安全运行的影响,采用扩展有限元法（eXtended Finite Element Method, XFEM）对其进行裂纹扩展分析,并结合正交实验法研究裂纹参数对扭杆强度的影响.结果表明：裂纹的长度对扭杆强度影响最大,裂纹的形状对扭杆强度影响最小.该数值分析方法可应用于扭杆的设计和检修中.     

The frequency partitioned block modified filtered-x NLMS with orthogonal correction factors for multichannel Active Noise Control

The Normalized Least Mean Square (NLMS) algorithm with a filtered-x structure (FxNLMS) is a widely used adaptive algorithm for Active Noise Control (ANC) due to its simplicity and ease of implementation. One of the major drawbacks is its slow convergence. A modified filtered-x structure (MFxNLMS) can be used to moderately improve the speed of convergence, but it does not offer a huge improvement. A greater increase in the speed of convergence can be obtained by using the MFxNLMS algorithm with orthogonal correction factors (M-OCF), but the usage of orthogonal correction factors also increases the computational complexity and limits the usage of the M-OCF in massive real-time applications. However, Graphics Processing Units (GPUs) are well known for their potential for highly parallel data processing. Therefore, GPUs seem to be a suitable platform to ameliorate this computational drawback. In this paper, we propose to derive the M-OCF algorithm to a partitioned block-based version in the frequency domain (FPM-OCF) for multichannel ANC systems in order to better exploit the parallel capabilities of the GPUs. The results show improvements in the convergence rate of the FPM-OCF algorithm in comparison to other NLMS-type algorithms and the usefulness of GPU devices for developing versatile, scalable, and low-cost multichannel ANC systems.     

蚁群生成树算法研究

应用蚁群生成树算法搜索了有34个节点的连接图的生成树,并采用正交设计法和均匀设计法进行了参数优化配置方法研究。结果表明:对于参数较多的蚁群算法,应用正交设计法和均匀设计法进行参数优化配置是一种可行且有效的途径,可有效提高蚁群算法的收敛速度,在求解精度上也有一定优势;充分发挥人类智能与仿生物智能的各自优势是克服单纯靠智能优化方法随机搜索缺点的关键;当蚂蚁数目为100、信息素相对重要性因素为0.3、信息素衰减系数为3.6、信息素挥发系数为0.4、信息素增加强度系数为14时,蚁群生成树算法效果最佳。     

百色水利枢纽大坝二等变形监测控制网测量

百色水利枢纽大坝初始变形监测控制网起算点遭到破坏,观测被迫中断,为了更好地对大坝进行监测,根据大坝及周围环境特点,针对现场复杂的测量条件,设计了大坝变形监测的二等基准控制网测量方案,采用测量机器人进行测量,并对外界条件的影响进行了改正。测量结果表明:测量控制网的测量精度较高,达到了预期目标。     

Performance of orthogonal STBC-MIMO with variable-power adaptive modulation and delayed feedback in Nakagami fading channels

A variable-power （VP） adaptive modulation （AM） scheme with space-time block code （STBC） is developed in MIMO systems, and the corresponding performance is investigated in Nakagami fading channels. The optimum switching thresholds are derived so that the spectrum efficiency （SE） under an average power and a target bit error rate （BER） constraint is maximized. By the switching thresholds, average BER and SE are further derived. As a result, closed-form expressions are obtained. Besides, the exact and approximate BER expressions of VP AM and constant-power （CP） AM systems with delayed feedback are respectively derived. Simulation results show that the theoretical SE and BER can match the corresponding simulation well. The results indicate that VP-AM with STBC provide higher spectrum efficiency than the CP counterparts, and has slighter bite error rate performance degradation when the normalized delay is less than 0.01.     

基于802.11n的WLAN安全解决方案研究

随着无线局域网技术的飞速发展,IEEE 802.11n是无线局域网技术的最新标准,介绍了基于802.11n的MIMO(多入多出)、OFDM(正交频分复用)和双频带等无线通信系统的关键技术,分析了在802.11n标准下WLAN的安全问题,通过数据加密、双向认证、动态WEP密钥和虚拟专用网络等方法,提出了基于802.11n的WLAN安全解决方案。     

基于正交化算法的均匀圆阵空时二维谱估计

本文讨论了阵列信号的谱估计问题,将G-S正交化算法用于均匀圆阵的空时二维谱估计中,研究了目标信号频率与到达角联合估计问题。通过仿真结果可以表明该方法与MUSIC算法相比,能更精确的估计目标信号的频率与方位角。     

基于改进RX算法的高光谱异常检测

针对RX算法中局部背景协方差矩阵估计的局限性,提出一种改进的RX (I-RX)异常检测算法。基于奇异值分解(SVD),将高光谱图像投影到背景的正交子空间上,获得仅包含噪声和异常的残留图像。在此基础上,通过计算各样本的空间秩深度将残留图像划分为噪声背景和潜在异常两个样本集,利用噪声背景集估计整幅图像的背景协方差矩阵,并将潜在异常集作为测试样本进行异常检测。对模拟数据和真实高光谱数据进行了实验仿真,ROC曲线表明,在相同的虚警概率下,I-RX算法的检测概率相较于RX平均提高了2倍左右。     

正交U变换及其快速算法

采用递推方法构造一种正交变换,称之为U变换,该变换含有分段常数基向量、分段一次多项式基向量以及分段二次多项式基向量,是对Walsh变换、斜变换的推广。根据递推方式,可以得到相应的快速算法。利用平移复制算子和Kronecher积的性质,推导基于Kronecher积的快速算法和正交U变换的直接分解算法。将该变换应用于图像压缩中,构造基于人类视觉系统的量化表,实验结果表明,正交U变换的图像压缩性能明显优于斜变换的图像压缩性能,与DCT变换的图像压缩性能相当,为图像压缩提供了一种新的选择。