基于Harr小波的时变谐波检测

电力系统中，实际的波形总存在不同程度的非正弦畸变。文中利用Harr小波对时变谐波进行检测。不是用Harr小波将信号分解到不同的频带上，而是利用该小波基对时变谐波的幅值和相角进行逼近。给出了电力系统时变谐波检测算法的推导及流程。通过仿真分析与对比，验证了此算法的可行性和精度。     

电力系统暂态信号分析中小波基的选择原则

讨论了电力系统中常见的暂态信号分析应用，如电力暂态信号检测、去噪与数据压缩以及暂态信号定位等，对这些应用中小波基的选择原则进行了系统的分析研究。研究结果表明，具有高阶奇异性的电力暂态信号必须选择具有相当消失矩的小波基；低频载波中检测弱暂态，应尽量选择中心频率较高的小波基；窄带干扰中提取暂态信号，应选择过渡带窄且具有良好分频能力的高阶小波；去噪、滤波和数据压缩方面，B系列小波具有更好的噪声抑制能力；电力系统故障暂态信号与峰值突变更接近，因此，在暂态信号定位时，一般应选择对称小波对故障暂态信号定位。应用中除选择恰当的小波基外，应根据被分析信号选择合适的分析尺度。     

GIS局部放电检测中的小波包变换提取信号

在介绍小波包变换算法的基础上，将小波包变换用于白噪声干扰下的气体绝缘组合电器（GIS）局部放电信号提取。对模拟的局部放电信号进行了小波包分解与重构的计算机仿真研究，分析了不同的局部放电波形、噪声水平及采样率对去噪结果的影响，最后对GIS内置传感器实测波形进行了小波包变换去噪。     

水电机组振动信号小波去噪参数优选方法研究

水轮机组振动信号在采集、传输和处理过程中不可避免地会引入噪声,要进一步处理信号必须进行去噪处理.小波去噪过程中小波和分解层数对去噪效果有很大影响,通常都按经验选取.本文提出一种针对具体水轮机组振动信号去噪时选择最优小波基和分解层数的方法.最终确定采用Db4小波分解5层对某机组上机架振动信号进行去噪,取得了良好的效果,分析得到最终去除的噪声为白噪声.     

基于Matlab的声发射信号小波滤噪研究

总结了基于Matlab的声发射信号小波滤噪的主要方法及主要阈值选取策略,其中包括各种方法和策略的Matlab指令,并从理论上指出了小波基、小波分解层数等因素的改变会对滤噪结果产生影响,最后对小波滤噪研究进行了展望。     

超高压电网故障录波数据自适应压缩新方法

综合分析了超高压电网变电站故障录波数据快速压缩传输的必要性，以及现有故障录波数据压缩传输算法的优缺点。提出了基于信号奇异性检测原理的自适应小波去噪压缩算法，详细分析了各尺度上小波系数奇异点的匹配搜索过程和最大尺度层数自适应阈值选取方法;通过故障录波信号频率与采样率的关系，确定出最大小波分解层数，然后在该分解层数上进行噪声白化检验，并对某一个信号奇异点进行奇异性指数计算，以确定出小波最优分解层数。最后通过大量真实故障录波数据编程仿真，验证了该压缩算法的高效性。     

小波包特征熵提取水轮机尾水管动态特性信息

将小波包多分辨与信息熵相结合,提出了一种故障检测与诊断的方法——小波包特征熵-故障法。首先对采集到的振动信号进行3层小波包分解,在通频范围内得到分布在不同频段内的分解序列,进而建立信号的小波包特征熵向量,选取最能反映故障特征的参数作为特征参数,进行故障诊断识别。以水轮机尾水管压力脉动信号为例,运用此法进行了尾水管动态特性信息提取。试验表明小波包特征熵法是提取故障信息并进行故障识别的一种行之有效的方法,为流体机械的故障诊断开拓了新的思路。     

基于水击波波形的波速反演方法试验研究

基于水击压力波的压裂诊断技术可用于快速判别裂缝位置，进而用于压裂工艺优选与施工参数优化。水击波波速是水击压力波诊断的关键参数，波速计算的读取方法对波速的准确性产生较大影响。为了精确计算水击波波速、减小波速变化引起的裂缝深度计算误差，搭建水击压力波试验系统，开展水平管路中压力波波速试验。使用4种方法计算压力波波速：描点读取压力突变点法、小波分解结合互相关函数法、描点读取水击周期法、基于频谱分析的水击周期法。以平均值、标准差及变异系数为指标，分析4种方法波速计算的数值结果与稳定性。在该试验中，针对10 kHz的采样频率，使用小波分解结合互相关函数法时优选出最优小波基函数为db4小波，最优分解层数为10层。使用双传感器计算的方法(描点读取压力突变点法与小波分解结合互相关函数法)得到的压力波波速高于单传感器计算得到的方法(描点读取水击周期法与基于频谱分析的水击周期法)。结果表明：双传感器法得到的波速范围为959.08 m/s至1111.11 m/s;单传感器法得到的波速范围为619.98 m/s至859.98 m/s。小波分解结合互相关函数方法在数据稳定性方面效果最好，可重复性最强；采用频谱分...     

基于小波变换检测谐波的新方法

首次将小波变换应用于电力系统谐波检测，通过对含有谐波的电流信号进行正交小波分解， 分析了电流信号的各个尺度上的分解结果。利用多分辨的概念，将低频段(高尺度) 上的结果看作不含谐波的基波分量。利用这种算法，可以利用软件构成谐波检测环节，同时 由于其计算速度较快，能够实时跟踪谐波的变化。     

平均插值小波在故障检测中的应用

现有小波基，如Symmlet小波、Meyer小波等在应用时，普遍存在边界效应，在实际应用中必须增加数据采集窗的宽度，即增加分析信号的数据量，才能加以消除。文中根据Donoho提出的构造平均插值小波基的方法，构造出2，4，6，8阶平均插值小波，利用其边界校正的优点，在对信号进行分析时，可自动消除“边界”现象，而且故障信号在变换域内能量更集中，可大大提高故障检测的准确性。实例证明，平均插值小波能较好地用于电力系统故障实时检测。     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

Impacts of Microcystis on algal biodiversity and use of new technology to remove Microcystis and dissolved nutrients

Cyanobacteria often dominate eutrophic lakes, outcompeting green algae that are required by fish and zooplankton. This study was undertaken to ascertain the impact of the cyanobacterium, Microcystis, on algal biodiversity. Under laboratory conditions, we found that the presence of Microcystis decreased phyla richness by 58%, phyla evenness by 47%, genera richness by 66% and genera evenness by 51%. Analysis by mixed anova s demonstrated a significant interaction between treatment and time and confirmed a significant reduction in richness and evenness of phyla and genera. We also conducted a phosphate restriction assay on the algae in Mason Lake (Irvine, CA, USA) and found that the threshold needed for algal growth there was 0.02 mg L^?1 PO₄. A pilot study was then conducted to test the effectiveness of the Blue Pro? water treatment facility in removal of this colonial organism from Mason Lake, in addition to removal of dissolved nutrients required for its growth. We measured a 97% reduction in Microcystis cells, a 72% reduction in chlorophyll‐a, and a 96% reduction in phosphate after just one 10 min cycle through the unit. Our study demonstrated that removal of Microcystis colonies may allow green algae to increase in numbers. This may improve algal biodiversity, which will benefit zooplankton and fishes.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

库水波动下库岸边坡地下水浸润线解析解及误差分析

解析法是库岸边坡地下水浸润线计算中便于实际应用的方法,但该方法须基于若干假定并对潜水运动基本方程线性化后才能求解。针对各假定和线性化过程建立不同的地下水渗流数学模型,用解析法和有限元法解答上述数学模型,分析各误差大小及其规律。结果表明：库岸垂直处理带来的误差要小于方程线性化处理和不考虑非饱和渗流带来的误差,而且它们都随渗透系数变大而减小;在三峡库区库水调度情况下,假定库水位等速变化带来的误差对大多岸坡而言可以忽略;计算库岸边坡地下水浸润线时,解析法只适用于水位变化幅度相比含水层厚度较小,且几何边界规则、岩土结构简单、岩土体渗透性较好时的情况。     

Changes in Summer Irrigated Crop Area and Water Use in Southeastern Turkey from 1993 to 2002: Implications for Current and Future Water Resources

Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based estimates of irrigation water requirements for cotton indicate a corresponding increase in agricultural water use from about 370 million cubic meters to over one billion cubic meters, a volume in accordance with the state estimates. These estimates have important implications for understanding the rapid changes in current agricultural withdrawals in Southeastern Turkey and form a quantitative basis for exploring the changes in future water demands in the region. For example, expansion of irrigated lands have led to a steady decrease in potential evaporation due to increased roughness and decreased humidity deficit in the Harran Plain. Assuming that the changes in future evaporation conditions will be of similar nature, water use for irrigation is expected to decrease over 40 percent in future irrigation sites. Incorporating this decrease in overall planning of the irrigation projects currently under construction should lead to improved management, and by extension, sustainability of water resources in the region.     

簸箕李引黄灌区水沙分布及优化调度的经验

灌区利用水沙观测所取得的资料和试验数据，运用水沙运动力学理论，总结分析和揭示了灌区水沙分布的规律和特点。在此基础上，结合灌区的实际运行情况，围绕减少骨干渠道的淤积进行探讨、研究，进而，优化水沙调度方案。该方案实施后，骨干渠道减旅伴效果明显，取得了成功的经验。