一种改进的早迟积分型位定时同步方法

数字通信系统中,位定时同步是实现正常数字通信的必要条件.位定时同步方法有很多,其中早迟积分型位定时方法是应用最广泛的位定时方法之一.本文基于传统的早迟积分型位定时方法,通过改进早迟积分环的鉴相器,提出了一种改进的早迟积分型位定时方法.经Matlab仿真表明,在相同的环路滤波参数下,改进的早迟积分型位定时方法的环路收敛速度最优可以提高2倍.     

Mode I–III Decomposition of the J‐integral from DIC Displacement Data

This paper presents the implementation of the decomposition method on digital image correlation (DIC) obtained displacement fields to obtain J‐integral results (J) and respective stress intensity factors (SIFs). DIC is increasingly used with the J‐integral approach in experimental mechanics to obtain J estimates from complex fracture processes. In this approach, the decomposition method is applied to DIC displacement fields for the first time. Here, displacement fields are separated before stresses and strains are computed, so that subsequent computation of separate J or SIF components may follow the classical full‐field J‐integral approach. The sensitivity of the decomposition method to experimental errors is investigated using synthetically generated errors imposed on crack tip displacement fields (Williams' series), from which improvements to the procedure are proposed. The method is experimentally tested on PMMA Arcan specimens under mode I, II, and III, and mixed‐mode I–III loading. Test results were compared to fracture toughness values obtained from ASTM tests and literature with close agreement.     

夹支扁球壳自由振动问题的准Green函数方法

将准Green函数方法应用于求解夹支任意形状底扁球壳的自由振动问题.即利用问题的基本解和边界方程构造一个准Green函数,这个函数满足了问题的齐次边界条件.采用Green公式将夹支任意形状底扁球壳自由振动问题的振型控制微分方程化为第二类Fredholm积分方程.通过边界方程的适当选择,积分方程核的奇异性被克服了.最后通过离散化方程求得数值结果.数值算例表明,该方法具有较高的精度,计算量小,收敛速度快,是一种新型有效的数学方法.     

基于自适应噪声模型和线积分卷积的铅笔画模拟

提出一种铅笔画模拟的方法.和传统的铅笔画步骤类似,经过轮廓提取和色调合成,产生铅笔画模拟图像.轮廓提取通过L0平滑后,用四向索贝尔算子提取边界,借助线积分卷积实现色调合成.与现存方法不同的是,给出一种自适应噪声模型,根据源图像产生自适应的噪声,将其作为线积分卷积的输入图像.实验证明提出的方法可以用来产生具有艺术效果的铅笔画模拟图像.     

集成成像三维新媒体的数字版权保护新方法

提出了一种新的基于集成成像的数字水印方法,利用集成成像机理和光学彩色图像的数字水印算法,实现了对集成成像三维新媒体的版权保护与内容鉴别认证,所提算法能满足稳健性和安全性的要求。通过实验,证明了所提方法的可行性和正确性,研究工作为集成成像三维新媒体的版权保护提供了新的思路与解决方法。     

全电坦克双向稳定系统自适应积分鲁棒控制

针对全电坦克双向稳定系统具有复杂的强非线性、强耦合性、强参数时变性等特点,提出了一种基于误差符号积分鲁棒反馈的坦克双向稳定系统自适应积分鲁棒(AIR)控制设计方法。考虑全电坦克双向稳定系统为一个耦合性的、非线性的、不确定性的动力学系统,建立面向真实的全电坦克双向稳定系统机电一体化解析动力学模型;基于Backstepping法融合自适应的思想,引入辅助误差信号设计了AIR控制器,有效衰减系统的未建模扰动;所设计的AIR控制器不需要预先知道未知扰动的上界,而是通过自适应的方法不断更新以获取其上界,降低了其工程应用的保守性;基于Lyapunov理论分析,在连续控制输入下可以保证坦克双向稳定系统获得渐进跟踪性能。通过Recurdyn-Simulink的仿真对比试验,验证所提方法的有效性。     

Finite element analysis of crack mouth opening displacement compliance in crack length evaluation for clamped single edge tension specimens

In the unloading compliance method developed for clamped single edge tension (SE(T)) specimens, six crack mouth opening displacement (CMOD)‐based compliance equations (i.e. a/W = f(BCE′)) were proposed for the crack length evaluation without clearly clarifying the corresponding predictive accuracies. In addition, the effective elastic modulus (E_e) that reflects the actual state of stress should also be introduced in the crack length evaluation for SE(T) specimens, because the actual state of stress in the remaining ligament of the test specimen is neither plane stress (E) nor plane strain (E′). In this study, two‐dimensional (2D) plane strain and three‐dimensional (3D) finite element analyses (FEAs) are carried out to investigate predictive accuracies of the six compliance equations. In both 2D and 3D FEA, specimens with a wide range of crack lengths and geometric configurations are included. For a given specimen, the value of E_e that presents the equivalent stress state in the remaining ligament is calculated on the basis of 3D FEA data. A set of formulae for the clamped SE(T) specimen is proposed that allows to evaluate E_e from the corresponding CMOD compliance. This approach is verified using numerical data. The observations of the numerical verification suggest that the use of E_e instead of E or E′ in CMOD‐based compliance equations markedly improves the accuracy of the predicted crack length for clamped SE(T) specimens.     

内爆法建筑倒塌过程和局部构件破坏数值模拟

为了探究内爆法拆除技术机理,通过混凝土本构MAT96,结合整体式建模对某建筑内爆法拆除的倒塌过程进行数值模拟,并对建筑物在倒塌过程中局部构件的破坏损伤情况进行分析研究,表明采用内爆法爆破拆除钢筋混凝土框架结构高层建筑物时,其倒塌过程强化了构件间相互的碰撞冲击挤压作用,能有效减少了结构体触地后的碰撞冲击能,被拆除建筑物的塌落振动效应也会随之降低,对于拆除爆破中结构构件破碎与解体的主要作用为构件间的碰撞冲击作用。     

温州永强机场新建航站楼项目主楼钢屋盖施工技术

温州永强机场新建航站楼项目主楼钢屋盖结构为网架结构,中部带有天窗张弦结构,本工程主楼钢屋盖投影面积达3.06万m2,采用地面分区拼装、合龙后整体提升、计算机同步控制、高空补缺的施工方案。从结构特点、安装重难点、钢结构的拼装及安装技术、施工监测、施工仿真模拟等方面进行了全面剖析。     

液压整体提升及下降技术在高空大跨度铝合金网壳施工中的应用

为保证跨度大、支撑少的高空铝合金网壳结构的顺利安装,先在地面构建一层措施钢平台以及与网壳相适应的高低不一的格构柱支撑系统,再通过液压整体提升技术将措施钢平台提升至预设高度进行铝合金网壳的安装以及卸载工作,然后通过液压整体下降技术将措施钢平台下降至地面进行拆除。该技术有效地解决了高空大跨度铝合金网壳施工难、风险高的问题,保证了对铝合金结构安装精度及施工应力的控制,同时也降低了措施钢平台高空装拆的风险。