A study on stress intensity factors and singular stress fields of three-dimensional interface crack

By using the finite-part integral concepts and limit technique, the hypersingular integrodifferential equations of three-dimensional (3D) planar interface crack were obtained; then the dominant-part analysis of 2D hypersingular integral was further used to investigate the stress fields near the crack front theoretically, and the accurate formulae were obtained for the singular stress fields and the complex stress intensity factors. After that, a numerical method is proposed to solve the hypersingular integrodifferential equations of 3D planar interface crack, and the problem of elliptical planar crack is then considered to show the application of the method. The numerical results obtained are satisfactory. Project supported by the Foundation of Solid Mechanics Open Research Laboratory of State Education Commission at Tongji University and the National Natural Science Foundation.     

Bandwidth‐efficient turbo coding over Rayleigh fading channels

Introduced in 1993, turbo codes can achieve high coding gains close to the Shannon limit. In order to design power and bandwidth‐efficient coding schemes, several approaches have been introduced to combine high coding rate turbo codes with multilevel modulations. The coding systems thus obtained have been shown to display near‐capacity performance over additive white Gaussian noise (AWGN) channels. For communications over fading channels requiring large coding gain and high bandwidth efficiency, it is also interesting to study bit error rate (BER) performance of turbo codes combined with high order rectangular QAM modulations. To this end, we investigate, in this paper, error performance of several bandwidth‐efficient schemes designed using the bit‐interleaved coded modulation approach that has proven potentially very attractive when powerful codes, such as turbo codes, are employed. The structure of these coding schemes, termed ‘bit‐interleaved turbo‐coded modulations’ (BITCMs), is presented in a detailed manner and their BER performance is investigated for spectral efficiencies ranging from 2 to 7 bit/s/Hz. Computer simulation results indicate that BITCMs can achieve near‐capacity performance over Rayleigh fading channels, for all spectral efficiencies considered throughout the paper. It is also shown that the combination of turbo coding and rectangular QAM modulation with Gray mapping constitutes inherently a very powerful association, since coding and modulation functions are both optimized for operation in the same signal‐to‐noise ratio region. This means that no BER improvement is obtainable by employing any other signal constellation in place of the rectangular ones. Finally, the actual influence of the interleaving and mapping functions on error performance of BITCM schemes is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Constellation constrained multiuser multiple‐input multiple‐output for high capacity and error performance over correlated fading channels

Channels' correlation has direct impact to degrade the capacity and reliability of multiple‐input multiple‐output (MIMO) systems considerably. In this paper, new signal constellation designs are investigated to mitigate fading correlation and maximize the capacity and error performance of multiuser MIMO (MU‐MIMO) over correlated channels, which is a major research challenge. Two methods are studied in a novel constellation constrained MU‐MIMO approach, namely, unequal power allocation and rotated constellation. Based on principles of maximizing the minimum Euclidean distance (d_min) of composite received signals, users' data can be recovered using maximum likelihood joint detection irrespective of correlation values. Compared with the identical constellation scenario in conventional MU‐MIMO, it is shown that constellation rearrangement of transmitted signals has direct impact to resolve the detection ambiguity when the channel difference is not sufficient, particularly in moderate to high correlations. Extensive analysis and simulation results demonstrate the superiority of proposed technique to capture most of the promised gains of multiantenna systems and application for future wireless communications. Copyright © 2014 John Wiley & Sons, Ltd.     

三维有限体中平片裂纹的超奇异积分方程方法—Ⅱ.数值方法

超奇异积分方程方法的理论分析已在本文的第Ｉ部分中给出，这一部分是经的数值方法，及用此方法求解的若干典型的平片裂纹问题。     

考虑法向压力梯度的三维旋转边界层计算

本文以量级分析为基础,建立了一般曲线坐标系上的三维旋转边界层方程。对旋转在边界层中的影响进行分析之后,提出了一个能够处理壁面法向压力梯度不为零问题的压力梯度迭代方法。在传统的Box法的基础上发展了一套完整的求解三维旋转边界层的方法和程序,并对螺旋面、压气机转子叶面以及圆柱面上的旋转边界层进行了计算,与他人的计算和实验的对比分析表明,该方法和程序是正确的,可用于求解任意几何物面上的三维旋转边界层。     

空腹式刚架拱桥梁拱节点三维光弹性试验研究

福州市尤溪洲闽江大桥是国内首座在拱肋（圈）上不设立柱和斜撑的空腹式刚架拱桥．作为空腹式刚架拱桥受力关键部位——梁与拱的连接部位，受力及构造复杂．通过三维光弹性试验，研究该梁、拱结合部的内力传递、应力集中、局部应力分布规律，为空腹式刚架拱桥节点设计、施工提供依据．     

基于虚拟仪器三维四翼混沌系统研究及实现

讨论了基于虚拟仪器三维四翼混沌系统的研究模式,设计了软件系统,并给出三维四翼混沌系统电路原理图及其实验结果,证实基于虚拟仪器技术为研究非线性系统提供可行的方案,利用此方案进行实验,结果证明此实验系统具有良好的实验效果。与传统的自治混沌系统相比,此系统具有参数调节方便、易实现、可靠性高,实时性好等优点,该特点在保密通信等工程中有重要的应用。     

离退休人员门诊规范化服务

该文对微机械气流式水平姿态传感器敏感机理进行了三维的有限元分析.利用ANSYS-FLOTRAN CFD软件,通过建模、划分网格、加载和求解等途径,计算了微机械气流式水平姿态传感器敏感元件密闭腔体中气流速度在不同倾斜状态下的分布.阐明微机械气流式水平姿态传感器的敏感机理,为气流式水平姿态传感器的优化设计开辟了更精确的研究途径.     

一种有效的角点检测与匹配算法

角点的检测和匹配是三维重建工作的基础部分,也是关系到三维图像重建准确性的重要部分。提出了一种角点检测算法,集多种经典算法之长处,用双重不同的判定条件,提高了的角点检测的速度,增加了检测出的角点数,并且改善了角点的精确度。在此基础上进一步提出使用简单的模板匹配方法进行角点匹配。实验表明,该算法简单且精确度高．优于其他现有的算法,而且能够得到足够多的匹配对进行下一步的三维重建工作。