白鹤滩水电站峡谷地形区的风特征研究

位居世界第二大的白鹤滩水电站地处金沙江下游峡谷区,频繁的大风给水电站建设和运行带来了严重影响。掌握水电站坝区大风变化规律,评估峡谷地形对风速的作用,有利于基于周围风场监测和预警峡谷区大风。根据水电站及周边观测资料,对坝区风的变化特征和峡谷地形作用进行了分析。(1)峡谷区最高频率的风向和最大平均风速的风向均为顺着峡谷的偏南风或偏北风,且偏北风频率达55%以上,峡谷锁定了流经气流。(2)坝区大风多发生在干季11月—次年5月,且夜间至清晨大风频率比日间高。干季峡谷风效应强,尤其在19时—次日08时。雨季峡谷风效应降低,局地山谷风增强,表现为山风比谷风持续时间长,08时和18时是山风和谷风交替时间。对应干季和夜晚大风频繁,说明峡谷风效应是影响大风的关键因子。(3)通过狭管效应分析马脖子和葫芦口大桥两个站之间的风速关系,表明峡谷地形使马脖子站风速加强为葫芦口大桥站的1.27倍。利用多种拟合方法建立的两站风速关系表明,当葫芦口大桥站为5m·s-1以下低风速,各方法都难以拟合峡谷区的风速,当风速在5.0～11.5m·s-1时,狭管效应对风速拟合最优,准确率超过70%,对11.5m·s-1以上强风速,多项式拟合效果较优,准确率接近65%。     

中低纬度系统相互作用过程的中尺度风场分析

以山东济南和滨州两部S波段多普勒雷达的观测数据为基础,采用直接合成的方法,反演台风“利奇马”和西风槽相遇引发极端降水过程的中尺度系统三维风场。（1）冷暖空气交汇产生的切变线长时间维持是西风槽与台风相互作用过程中产生极端降水的关键,暖空气先进后退,表现为东南气流和西北气流先后越过雷达站,垂直方向出现复合切变;（2）最强上升运动出现在对流单体回波梯度最大的区域,最大下沉运动出现在回波顶下风方,中低层回波中心均为弱风速区;（3）发展中的对流单体各层均有气旋式入流,成熟的对流单体高层出流有反气旋式出流;（4）风垂直切变是雨团降水增幅的主要影响因素,成熟期的雨团具有低质心对流单体风暴的结构形态,垂直运动达到最强。     

基于数值模拟的大口径高精度射电望远镜台址风障优化设计研究

随着射电望远镜口径增大、观测频率提高, 对其指向精度的要求也越来越高. 然而, 望远镜服役于野外台站, 台址风扰对天线指向精度的影响在高频段观测时已不能忽略. 由于风扰的时变性, 现有的抗风方法无法保障大口径高指向精度望远镜在高频段的有效观测时长. 因此, 提出了一种基于风障精确布置改善台址风环境的方法. 通过数值模拟构建了风障仿真模型, 并将仿真结果与风洞实测数据比较, 两种孔隙率风障的平均误差分别为3.7%和6.1%, 保证了风障模型的可靠性. 以新疆奇台射电望远镜(QiTai radio Telescope, QTT)台址为例, 基于QTT台址斜坡地形构建了计算域模型, 开展单风障不同高度、不同孔隙率的系列风场仿真试验, 得到了风障参量与下游挡风效果的关系. 基于单风障合理高度和最优孔隙率设置南北风障, 仿真结果表明在确定高度下最优孔隙率可以组合, 孔隙率0.1-0.1组合的风障挡风效果最优, 南方向来风在天线区域可以有效降低75%以上的风速.     

Neural network wind retrieval from ERS-1/2 scatterometer data

1IntroductionSatellite observations of the ocean,includingobservation of sea surface wind fields,have tendedto be a perfect technology.Scatterometer is a prima-ry remote sensing sensor,which can get the globalscale information of wind.Other means of remot…     

辽宁沿海地区风能资源状况及开发潜力初步分析

主要采用风电场的实测风资料,初步分析了辽宁沿海地区的风能资源特征及开发潜力。结果表明:辽宁沿海岸一带为风能资源丰富区和较丰富区,辽东湾沿岸风资源较黄海北部沿岸更为优越,风资源条件上具有更大的开发潜力;海岸到内陆风速迅速减少,离海岸稍远的陆上以辽东半岛顶部和辽河平原地区风速较大;沿岸50m高处风能资源较10m高处多1倍以上,年有效风力时数超过70%,表明辽宁沿海地区具有大规模开发利用风能资源的潜力,适合建大型风电场,且风电场离海岸越近越好。     

Foliar Particulate Matter Distribution in Urban Road System of Beijing,China

Particulate matter(PM), one of the most important pollutants of traffic emission, threatens the health of urban ecosystems and citizens. Roadside trees play an important role in trapping PM, and the foliar PM load is a useful indicator for air PM pollution in road systems. To detect the relationships of foliar PM load with road structures, urbanization, and meteorology in road systems, we studied a widely-planted tree Sophora japonica L. in 100 roads and 10 yards of Beijing, China, and found that the foliar PM loads increased with the distances from the urban centre(DUC) linearly, while decreased with the road density. All-subsets regression analysis indicated that DUC, average monthly relative humidity, average monthly wind speed, and mean annual wind speed were the most important factors in predicting foliar PM load, rather than general situation of buildings and road cleanliness. The monthly relative humidity and monthly wind speed had a negative correlation to foliar PM, while the annual relative humidity and annual wind speed had a positive correlation to foliar PM. Suburban areas and these effective factors should be highlighted in PM control in Beijing.     

基于FY-2遥感数据的台风中心定位

针对台风在形成和消散阶段中心定位准确率较低的问题,本文提出了一种基于云导风的方法,使用的遥感数据来源于FY-2气象卫星的红外通道。该方法首先对红外序列遥感图像进行金字塔分解,然后基于加权的中值滤波光流模型构建云导风场,最后利用密度矩阵计算台风中心。选择2014年真实形成于西北太平洋的台风Rammasun和Halong进行案例分析,结果表明该方法对台风整个生命周期阶段的检测结果均较准确。     

Un- and reloading stiffness of monopile foundations in sand

The eigenfrequency of offshore wind turbine structures is a crucial design parameter, since it determines the dynamic behavior of the structure and with that the fatigue loads for the structural design. For offshore wind turbines founded on monopiles, the rotational stiffness of the monopile-soil system for un- and reloading states strongly affects the eigenfrequency. A numerical model for the calculation of the monopile’s behavior under un- and reloading is established and validated by back-calculation of model and field tests. With this model, a parametric study is conducted in which pile geometry, soil parameters and load conditions are varied. It is shown that of course the rotational stiffness varies with mean load and magnitude of the considered un- and reloading span, but that for most relevant load situations the initial rotational stiffness of the monopile system, i.e. the initial slope of the moment-rotation curve for monotonic loading, gives a good estimate of the actual stiffness. Comparisons of different p–y approaches show that the ordinary API approach considerably underestimates the initial stiffness, whereas the recently developed ‘Thieken’ approach and also the ‘Kallehave’ approach give a much better prediction and thus might be used in the design of monopiles in sand.     

Aeolian sand transport at the Lanphere Dunes,Northern California

Aeolian sand transport was studied at the Lanphere Dunes, a coastal dune complex in northern California, by comparing slipface advance rates with transport predicted based on local wind data. The slipfaces of a 2·5 m high transverse ridge and 10 m high parabolic dune were monitored over a period of three months to estimate sand discharge. The study was performed during the dry season, which has the maximum sand‐driving potential. Over the three month study period, average sand discharge was 12·5 m³ per m width per year at the transverse ridge and 8·8 m³ per m width per year at the parabolic dune. A method was developed for modelling slipfaces that are sinuous and where sediment transport rates are not constant across the width of the slipface. Field measurements were used to generate three‐dimensional representations of dune slipfaces. Periodic measurements over the course of three months were used to compute the volume of displaced sediment. Theoretical sand transport was computed from local wind data using the Bagnold model and compared with the observed transport rates. Predicted rates were substantially lower than observed rates. Wind velocities rarely exceeded the threshold velocity. Discrepancies between the observed and predicted values appear to be caused by a combination of wind data recording procedures and differences between wind velocities at the anemometer location and the site where sand transport was measured. Wind data collected by weather bureaux have been utilized in numerous studies for modelling sediment transport. Such data typically have sample intervals of one hour or greater and are often averaged prior to reporting. The effect of averaging was investigated by comparing sand transport estimates based on daily average wind velocities with those based on the original hourly observations. The daily average data were depleted of high velocity winds and sand transport estimates were accordingly much lower than those based on the hourly data. Copyright © 2000 John Wiley & Sons, Ltd.