一种带宽约束的无线传感器网络节点调度算法

研究了无线传感器网络在带宽受限时怎样最小化覆盖裂口,同时最大化网络生命期的问题。将带宽限制理解为活动节点的活动邻居数限制,且认为由于带宽约束,当需要的带宽大于实际能提供的带宽时,覆盖裂口就可能发生。进而提出了一种最小覆盖裂口的混合整数规划模型,并提出了一种求解此问题的启发式算法,同时也研究了带宽和节点数对网络覆盖的影响。仿真实验表明,增加节点数可延长网络的生命期,增加带宽可减少裂口的发生,这与理论分析的结果是一致的。     

面向机械振动监测的无线传感器网络节点的设计

针对机械振动信号监测的特点和现有无线传感器网络节点的不足,提出了一种基于MEMS加速度传感器的无线传感器网络大容量测振节点的设计.节点采用了模块化的设计思想,主要包括AVR微控制器、可编程逻辑器件CPLD、多通道16位A/D转换器、SD卡存储器和MEMS传感器,初步解决机械振动信号采集和大容量存储的难题.通过实验验证了该设计方案的可行性.     

A box scheme for transcritical flow

The accurate computer simulation of river and pipe flow is of great importance in the design of urban drainage networks. The use of implicit numerical schemes allows the time step to be chosen on the basis of accuracy rather than stability, offering a potential computational saving over explicit methods. The highly successful Box Scheme is an implicit method which can be used to model a wide range of subcritical and supercritical flows. However, care must be taken over the modelling of transcritical flows since, unless the correct internal boundary conditions are imposed, the scheme becomes unstable. The necessity of accurately tracking all the critical interfaces and treating them accordingly can be algorithmically complex and in practice the underlying mathematical model is often modified to ensure that the flow remains essentially subcritical. Such a modification however inevitably leads to additional errors and incorrect qualitative behaviour can be observed. In this paper we show how the technique of ‘residual distribution’ can be successfully implemented in order to accurately model unsteady transcritical flow without the need to know a priori which regions of the computational domain correspond to subcritical and supercritical flow. When used in conjunction with a form of artificial smoothing, the resulting method generates very high resolution results even for transcritical problems involving shocks, as can be seen in the numerical results. Copyright © 2002 John Wiley & Sons, Ltd.     

A study of a commercial MHD power plant scheme

Power engineering specialists are currently interested in electrical power stations with magnetohydrodynamic generators. This interest has been generated by the fact that fossil fuels are becoming increasingly costlier, and with the exploitation of remote and practically inaccessible deposits, a more rational utilisation of fuel has become necessary. Research on magnetohydrodynamic generators is being conducted in many countries at present. In the USSR a composite pilot plant with an MHD generator whose output exceeds 20 MW has already been operative for several thousand hours. However the pilot plant has to be considerably modified to serve as a model for the 500–1000 MW industrial power unit. This paper is devoted to an investigation of one of the possible process flow diagrams of MHD electrical power plants. The structure of MHD electrical power plants, the interrelation between the aggregates, issues concerning the starting of the plant and the working of the power unit under various partial load conditions are discussed. With the availability of new theoretical and experimental data, the process flow diagrams of industrial MHD electrical power plants will naturally undergo changes. However, the methodical approach and the investigations, described in this paper should retain their validity for all process flow diagrams of electrical power plants with MHD generators.     

山区铁路沿线泥石流次声监测预警方法

在了解国内外泥石流次声监测方法及技术的基础上,探讨了可同时记录信号过程的DBF-IS泥石流次声监测警报仪研制及其监测系统构建原理和方法。DBF-IS泥石流次声监测仪主要功能是监测、采集泥石流发生时的次声特征频率、主频振幅及持续时间等信息,该仪器便于安装和维护,适合山区铁路沿线泥石流监测预警。泥石流次声监测预警系统则是由次声监测终端及中心计算机系统组成,监测终端可同时发出灾害预警及进行信息传输;中心计算机系统实现监测点参数信息设置管理、数据通讯、数据处理及泥石流预警等功能。该山区铁路沿线泥石流次声监测预警系统能实现泥石流发生位置准确定位和大致发生规模,并根据监测到的泥石流次声信息及时向铁路相关部门发出预警信号,确保列车运营安全。     

面向机械振动信号采集的无线传感器网络节点设计

针对现有无线传感器网络节点的不足和机械振动信号采集的需求,设计了一种可实现机械振动信号采集和片上处理的无线传感器网络节点。该节点采用MEMS加速度传感器拾取振动信号,以低功耗FPGA芯片为控制核心,采用了可编程片上系统技术,将数据采集、存储、处理和传输等控制功能模块集成到单个FPGA芯片中。本文着重介绍了节点数据采集、存储和传输部分的硬件电路和控制逻辑设计,对比实验表明该节点能有效采集和监测机械振动信号。     

水石流冲击信号能量分布试验研究

泥石流冲击谱是泥石流固液两相介质运动特性的综合表征,探索泥石流冲击信号的能量大小及其分布特性是合理确定泥石流冲击荷载的关键环节。运用自行研制的试验模型,实施了15种试验工况的泥石流冲击试验,获取了85 000多个测试数据。依据固相比为0.16、粒径组为0.8～1.5 cm水石流冲击测试结果,运用db8小波基变换对试验结果进行8层小波分解,得到频率范围分别为0～0.195Hz,0.195～0.391 Hz,0.391～0.781 Hz,0.781～1.562 5 Hz,1.563～3.125 Hz,3.125～6.25 Hz,6.25～12.5 Hz,12.5～25 Hz和25～50 Hz共九个频率段的冲击信号,据此揭示了不同频段冲击信号能量分布规律。从低频段至中高频段水石流冲击能量非线性衰减,90%以上的冲击能量分布在小于0.195 Hz的低频部分;水石流在中高频段的冲击能量总体呈衰减分布,但在频段三和频段六出现较显著峰值,表明水石流也存在一定阵流现象;水石流中固相粒径越小,低频段至高频段的冲击能量衰减速度越慢。研究成果可为进一步实施泥石流冲击荷载精细实验研究提供一定科学依据。     

基于局部网络拓扑特征的鲁棒节点定位算法

针对无线传感器网络的较大测距误差严重影响定位算法精度和鲁棒性的问题,利用节点均匀部署网络的拓扑特征,提出了一种基于局部网络拓扑特征的鲁棒节点定位算法(LFLS算法).该算法通过构建节点测距高估粗差阈值参数和测距低估粗差阈值参数,在对未知节点1跳测距数据集进行粗差识别及剔除等预处理滤波的基础上,使用高斯加权最小二乘定位算法实现节点定位.仿真结果表明,基于局部网络拓扑特征的鲁棒节点定位算法的定位精度明显优于未采用局部网络拓扑特征进行粗差预处理的加权最小二乘定位算法,其中粗差测距直接相关节点的定位精度改进尤为明显.     

Photovoltaics in the assessment of wireless sensor network reliability with changing environmental conditions

This paper presents a reliability assessment of a wireless sensor network (WSN) equipped with mini photovoltaic cells (PV‐WSN) under natural environmental conditions while accounting for different types of system failures. In particular, our assessment considers the hardware specifications of the sensors, photovoltaic (PV) specifications, the use of rechargeable batteries, communication protocols, and various elements required for efficient detection of environmental conditions. We accomplished this by developing a simulator that generated data for 2 broad WSN conditions: (1) WSN without PV and (2) WSN with PV. The dynamic source routing protocol was employed for these simulations, and the following variables were assessed for both conditions: WSN reliability, the impact of energy consumption on the network, and the types of failures that lead to sensor unavailability. The following assumptions were made to run the simulation: the distribution of WSN nodes is random, with 1 sink node per rectangular cluster, the sensor nodes are structurally and functionally identical, environmental interference and suboptimal orientation impair PV cell recharge capacity randomly, and no communication loss occurs. Our reliability assessment assumed extreme environmental conditions and further made assessments of component reliability that included the following parameters: sensor and PV cell hardware specifications, the rechargeable nature of PV cell batteries for different sensor activity states, the availability of sunlight for powering PV cells, and the energy efficiency of PV cells. We found that network lifetime was prolonged for the PV‐WSN condition over the WSN without PV condition, introducing a role for PV cells as potential energy sources for WSNs.     

时间异步无线传感器网络的目标跟踪动态成簇算法

为了解决时间异步无线传感器网络在目标跟踪时的节点协作管理和跟踪时间配准问题,提出了一种适用于时间异步条件下目标跟踪的动态成簇算法。该方法通过分析目标的无线信号强度和各节点至目标的距离来动态组建跟踪簇,然后依据目标及簇头的通信距离对簇头射频信号的覆盖区域进行功能划分,实现节点对目标的协作跟踪,同时以簇为跟踪时间的计算单元,通过簇内计时和簇间贯序传递的方法实现跟踪时间的配准。仿真实验表明,该算法进行目标跟踪时能有效均衡网络能耗,且具有较好的跟踪精度和系统鲁棒性。     

Modal power flow with application to damage detection

Features of power flow of an undamped beam at resonance are studied in the present paper. It is found that when an undamped beam undergoes free vibration at one of its natural frequencies, the active component of the power flow becomes zero while the reactive component is of modal pattern, whose characteristic frequency is twice of the natural frequency. The power flow in this case can thus be termed as modal power flow. The instantaneous energy density associated with the vibration mode consists of a static component and a dynamic component, related to the mean total and Lagrangian energy densities, respectively. The modal power flow is relevant to the latter but independent of the former. Potential application of modal power flow to structural damage detection is investigated. Two typical damages, transverse cracks and delaminations, are considered. A damage index based on the modal power flow is proposed, and compared with the damage indices based on the slope, the bending strain, and the strain energy through numerical examples. The imperfection of boundary conditions is also considered. It is shown that the proposed damage index is sensitive to both types of damage, thus can be used as an universal damage indicator.     

适于泥石流除噪的EMD联合小波阈值除噪方法

次声传感器采集到的泥石流次声信号中包含有大量的无关干扰信号,严重影响信号的分析与评估。针对含噪泥石流信号中无法准确确定噪声频段的特点,以及传统经验模态分解(Empirical Mode Decomposition, EMD)联合小波阈值去噪方法无法智能分辨噪声所在频段的缺点,提出了信号经EMD分解后,基于相关性选择噪声频段的方法。首先利用EMD分解获取信号的固有模态函数(Intrinsic Mode Function, IMF)分量,然后计算各个IMF分量与原始信号的相关性,根据相关性大小确定IMF噪声频段,然后采用小波阈值去噪方法对噪声频段进行处理,最后对处理后的信号进行重构得到去噪泥石流信号。通过模拟实验分析,证明该方法具有智能选择噪声频段的能力,是一种更适于泥石流信号的去噪方法。     

用于无线传感器网络的光伏微能源系统设计

微型传感器节点通常采用能量有限的电池供电,电池的使用寿命限制了传感器节点的寿命.针对传感器网络的特征和需求,设计了光伏微能源系统,并与微型传感器节点集成,形成自供电的微系统.光伏微能源系统主要包括光伏电池、聚合物锂电池和能源管理子系统.本文阐述了光伏微能源系统的设计,并对微系统的实验测试结果进行了分析.实验结果证明,光伏微能源系统能够自行补充能量,延长传感器网络的使用寿命.     

超低功耗无线数字温度传感器的研制

研制了一种低功耗、电池供电的无线数字温度传感器。此传感器以PIC16F73单片机、数字温度传感器DS18B20、单片射频收发芯片nRF901为核心，工作频率433MHz，测温范围-400℃～85℃，分辨力为0．0625℃，测温精度0．5℃，静态电流小于8μA，动态电流小于0．75mA，在市区环境中，可靠通信距离40m。     

Development of a wireless radioactive material sensor network

Our team at the United States Army Research Laboratory (ARL) has designed and developed a low-power, compact, wireless-networked gamma sensor (WGS) array. The WGS system provides high sensitivity gamma photon detection and remote warning for a broad range of radioactive materials. This sensor identifies the presence of a 1 μCi Cs137 source at a distance of 1.5 m. The networked array of sensors presently operates as a facility and laboratory sensor for the movement of radioactive check sources. Our goal has been to apply this architecture for field security applications by incorporating low-power design with compact packaging. The performance of this radiation measurement network is demonstrated for both detection and location of radioactive material.     

水润滑轴承水膜压力无线监测节点供电方法研究

针对水润滑轴承水膜压力无线监测节点的供电问题,提出一种旋转能量收集方法并设计能量收集装置.旋转能量收集方法应用永磁发电机将转轴旋转产生的机械能转化为电能,并由能量收集装置(整流、降压、充电管理电路与锂电池)将电能进行转换与存储后为节点在线供电.首先对能量收集装置中的各电路进行仿真,然后建立节点能量模型并对节点能耗进行分...     

基于距离分区的多级异构无线传感器网络成簇算法

为了防止无线传感器网络(WSN)节点因为通信距离过长而过早死亡,有效延长网络生命周期,提出了一种基于距离分区的高能效的多级异构无线传感器网络成簇算法(MHCADP)。此算法将监测区域分为三部分,并根据不同监测区域和基站的距离部署能量不同的三类节点,按照节点剩余能量与网络平均能量的比例来选举簇头节点,让较高初始能量和剩余能量的节点拥有更多的机会成为簇头。另外,在数据传输时,考虑节点和基站的距离以及自身剩余能量,选择单跳或多跳的传输方式。仿真实验结果表明,与现有的重要成簇算法——低能耗自适应分簇分层(LEACH)算法和稳定选举协议(SEP)算法相比,MHCADP算法能够有效减少网络能量消耗和平衡网络负载,使网络稳定周期和生命周期延长50%以上。     

Monitoring a PGD solver for parametric power flow problems with goal‐oriented error assessment

The parametric analysis of electric grids requires carrying out a large number of power flow computations. The different parameters describe loading conditions and grid properties. In this framework, the proper generalized decomposition (PGD) provides a numerical solution explicitly accounting for the parametric dependence. Once the PGD solution is available, exploring the multidimensional parametric space is computationally inexpensive. The aim of this paper is to provide tools to monitor the error associated with this significant computational gain and to guarantee the quality of the PGD solution. In this case, the PGD algorithm consists in three nested loops that correspond to (1) iterating algebraic solver, (2) number of terms in the separable greedy expansion, and (3) the alternated directions for each term. In the proposed approach, the three loops are controlled by stopping criteria based on residual goal‐oriented error estimates. This allows one for using only the computational resources necessary to achieve the accuracy prescribed by the end‐user. The paper discusses how to compute the goal‐oriented error estimates. This requires linearizing the error equation and the quantity of interest to derive an efficient error representation based on an adjoint problem. The efficiency of the proposed approach is demonstrated on benchmark problems. Copyright © 2016 John Wiley & Sons, Ltd.     

泥石流冲击荷载下拦挡坝的动力响应分析

选取典型的泥石流冲击荷载,把钢筋混凝土拦挡坝简化成悬臂梁,建立其动力偏微分方程,运用数学物理方程中的变量分离法和结构动力学中的振型叠加法求得动力偏微分方程的解析解,最后根据材料力学得到相应的应力以及应变。算例分析表明解析解是可靠的,且在拦挡坝的坝顶处有最大的位移,为实际工程力学计算提供一种思路。       

A fully explicit characteristic based split (CBS) scheme for viscoelastic flow calculations

In this paper, an explicit characteristic based split (CBS) scheme is proposed for the numerical solution of incompressible viscoelastic flow equations. The scheme proposed is free from simultaneous solution to the matrices arising from the finite element discretization of the governing equations. The experience gained from the solution of Newtonian fluid dynamics problems has been applied to the solution of viscoelastic flows. The Oldroyd‐B model has been employed to solve two benchmark problems of viscoelastic flow. They are viscoelastic flow past a circular cylinder and viscoelastic flow through planar contraction geometry. The results show that the solutions obtained are stable for the Weissenberg or Deborah number range studied in this paper. The solutions obtained at lower Weissenberg or Deborah numbers are accurate and agree excellently with the majority of available numerical data. However at higher Weissenberg or Deborah numbers, results show some sign of negative influence of the artificial dissipation added to the discrete constitutive equations. Copyright © 2004 John Wiley Sons, Ltd.