二维圆环结构中弹性波传播的谱单元分析

为研究弹性波在结构中的波场特征,推导建立一种任意四边形二维谱单元,将其应用于二维圆环结构中的波传播行为模拟.以矩形平板结构中弹性导波传播分析为例,通过与传统有限元分析结果对比,验证所建立谱单元的有效性.有裂纹和无裂纹二维圆环结构谱单元模拟结果表明:弹性波在圆环结构中传播会发生频散;圆环结构表面的裂纹对瑞利波的传播影响最大;根据其反射波包位置可以确定损伤位置.     

光伏微逆变器电流传感器和功率管开路故障诊断

当电流传感器出现性能蜕化、故障或失效时,光伏微逆变器系统的输出会受到严重影响,甚至微逆变器系统其他部件有可能被直接损坏而导致整个系统永久失效;微逆变器系统中反激式变换器功率管的开路故障会引起2个交错支路电流不平衡,导致输出电流波形畸变率变大.为此,提出一种基于状态观测器的光伏微逆变器电流传感器和功率管开路故障诊断方法.建立两路反激式变换器的数学模型;构建状态观测器以实现对两路反激式变换器原边电流的在线估计,并生成残差;将残差与阈值进行比较,实现对微逆变器系统中电流传感器与功率管的实时故障诊断.仿真结果验证该方法可行且有效.     

远程可视化遥控侦察定位机器人系统设计

远程可视化遥控侦察定位机器人系统共由两部分构成.第一部分为机器人,与PC远程控制终端建立网络连接,获取控制命令,解析命令后控制机器人的运动电机、转向舵机和立体视频云台.机器人将自己的GPS位置信息和环境图像传输到PC控制终端.第二部分为PC远程控制终端,获取北通遥控手柄的命令数据并打包后,通过网络传输给机器人,实现机器人运动状态控制.PC远程控制终端通过网络获取机器人的GPS位置数据和视频数据,将数据解析后分别显示到图像监控窗口和地图定位窗口.     

Fault estimation observer design for discrete‐time systems in finite‐frequency domain

This paper proposes a framework of fault estimation observer design in finite‐frequency domain for discrete‐time systems. First, under the multiconstrained idea, a full‐order fault estimation observer in finite‐frequency domain is designed to achieve fault estimation by using the generalized Kalman–Yakubovich–Popov lemma to reduce conservatism generated by the entire frequency domain. Then, a reduced‐order fault estimation observer is constructed, which results in a new fault estimator to realize fault estimation using current output information. Furthermore, by introducing slack variables, improved results on full‐order fault estimation observer and reduced‐order fault estimation observer design with finite‐frequency specifications are obtained such that different Lyapunov matrices can be separately designed for each constraint. Simulation results are presented to illustrate the advantages of the theoretic results obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimal controller location in wireless networked control systems

The control performance of wireless networked control systems (WNCS) has been shown to heavily depend on the packet delivery quality of both the sensor‐to‐controller and controller‐to‐actuator communications. Such quality relies on the relative distance between the wireless transmitter and receiver, which naturally raises the challenging problem of controller placement in WNCS for optimal control performance. In this paper, we investigate the optimal controller location (OCL) problem in WNCS based on linear‐quadratic‐Gaussian control strategy. For the one‐hop network case where the controller can only be placed at either the sensor side or the actuator side, we derive a simple yet effective criterion to determine the OCL. For the more general multi‐hop case where the controller can be located at either one of the sensors, relays, or actuators, we obtain the necessary and sufficient condition under which the closed‐loop system is guaranteed to be stable. On the basis of these results, we further transform the OCL problem into an optimization problem that can be solved efficiently. Numerical results are provided to verify our analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Design of a printed log‐periodic dipole array antenna with high gain for millimeter‐wave applications

In this article, a V‐band printed log‐periodic dipole array (PLPDA) antenna with high gain is proposed. The antenna prototype is designed, simulated, fabricated, and tested. Simulation results show that this antenna can operate from 42 to 82 GHz with a fractional impedance bandwidth of 64.5% covering the whole V‐band (50–75 GHz). The antenna has a measured impedance matching bandwidth that starts from 42 to beyond 65 GHz with good agreement between the experimental and simulated results. At 50 and 65 GHz, the antenna has a measured gain of 10.45 and 10.28 dBi, respectively, with a gain variation of 2.6 dBi across the measured frequency range. The antenna prototype exhibits also stable radiation patterns over the operating band. It achieves side‐lobe suppression better than 17.26 dB in the H‐plane and better than 8.95 dB in the E‐plane, respectively. In addition, the cross‐polarization component is 18.5 dB lower than the copolarization with front‐to‐back ratio lower than 24.1 dB in both E‐ and H‐planes across the desired frequency range. Based on a comparison of performance among the reported work in the literature, we can say that the proposed PLPDA antenna is a proper candidate to be used in many applications at V‐band frequency. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:185–193, 2015.     

Optimistic Byzantine fault tolerance

The primary concern of traditional Byzantine fault tolerance is to ensure strong replica consistency by executing incoming requests sequentially according to a total order. Speculative execution at both clients and server replicas has been proposed as a way of reducing the end-to-end latency. In this article, we introduce optimistic Byzantine fault tolerance. Optimistic Byzantine fault tolerance aims to achieve higher throughput and lower end-to-end latency by using a weaker replica consistency model. Instead of ensuring strong safety as in traditional Byzantine fault tolerance, nonfaulty replicas are brought to a consistent state periodically and on-demand in optimistic Byzantine fault tolerance. Not all applications are suitable for optimistic Byzantine fault tolerance. We identify three types of applications, namely, realtime collaborative editing, event stream processing, and services constructed with conflict-free replicated data types, as good candidates for applying optimistic Byzantine fault tolerance. Furthermore, we provide a design guideline on how to achieve eventual consistency and how to recover from conflicts at different replicas. In optimistic Byzantine fault tolerance, a replica executes a request immediately without first establishing a total order of the message, and Byzantine agreement is used only to establish a common state synchronization point and the set of individual states needed to resolve conflicts. The recovery mechanism ensures both replica consistency and the validity of the system by identifying and removing the operations introduced by faulty clients and server replicas.     

超声声辐射力弹性成像中基于拉东变换的剪切波速度估计方法的改进研究

能够无创定量测量人体组织弹性模量的声辐射力脉冲超声弹性成像方法,已经逐渐成为进行肝硬化分期和乳腺癌良恶性判别等临床诊断的重要工具。但是,在临床实践中也发现,弹性模量测量的稳定性会受到测量深度和组织各向异性等多种因素的影响。因此,如何通过算法的改进提高声辐射力脉冲超声弹性成像测量结果的可靠性,一直是该领域所关注的重要课题之一。文章对现有的基于拉东变换的剪切波速度估计算法进行了多种方式的改进,并利用自主研发的声辐射力定量超声弹性成像系统所采集的超声射频数据,对几种方法得出的剪切波速度测量结果进行了比较。这些改进算法可以被分为两类：(I)在以“时间-侧向位置”为坐标的位移矩阵上进行拉东变换;(II)在以“时间-深度”为坐标的位移矩阵上进拉东变换。第一类算法试图找到在某一个特定深度上剪切波侧向传播的最佳拟合轨迹,而第二类算法则试图直接找到在整个测量深度范围内,剪切波波前通过每个侧向位置的准确时间点。文章在标准弹性仿体和离体猪肉组织样本上进行了测量实验,比较了在不同深度位置上重复测量结果的可靠性,以及这些算法的耗时情况。实验结果将有助于我们找到一种兼顾测量稳定性和计算速度的新型剪切波速度估计算法,并将其应用到声辐射力脉冲超声弹性成像中,提高其测量结果的可靠性和在临床应用中的价值。     

岩土体开挖变形的分步模拟方法及其工程应用

本文提出了一种岩土体开挖变形的分步模拟方法;该方法以岩土体弹塑性参数和现场变形监测数据为基础,以开挖、施加支护等工程措施的实施为时间节点,以弹塑性荷载分步释放来表征岩土体荷载逐步释放的过程,模拟了岩土体开挖和支护前、后的变形效果,并近似地模拟出锚固、衬砌等措施的应力、变形状态,将岩土体复杂的粘弾塑性问题转化为了较简单的弹塑性问题。运用该方法模拟了涔天河水利枢纽右岸进口段密集洞室群的施工开挖和支护全过程,获取了施工过程中围岩的应力、变形及稳定特征,同时结合数值模拟的成果给出了相应的工程施工建议,可为工程的快速化施工提供参考。     

电波流速仪流量自动在线监测装置设计与应用

电波流速仪因其在测量过程中不受水情、含沙量及水面漂浮物的影响,因此近年来在水文部门得到了广泛应用。介绍了一种电波流速仪流量自动在线监测装置的设计方案,包括监测装置硬件和软件实现过程。将该装置应用于四川内江水文站实际测流工作,结果表明,使用电波流速仪的自动在线监测装置测流结果可靠,有利于提高效率和降低成本。可推荐类似水文测站采用。