The Structure of A Turbulent Jet in A Crossflow-Effect of Jet-Crossflow Velocity     

李行伟  匡翠萍  陈国谦 《中国海洋工程》2002,(1)

A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentr  相似文献   

Time changes in fishing power in the Danish cod fisheries of the Baltic Sea     

Marchal  Paul; Nielsen  J. Rasmus; Hovgard  Holger; Lassen  Hans 《ICES Journal of Marine Science》2001,58(1):298-310

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Ecology of beach wrack in northern New England with special reference to Orchestia platensis     

Manaf I. Behbehani  Robert A. Croker   《Estuarine, Coastal and Shelf Science》1982,15(6)

The northern New England beach wrack community with special reference to the cosmopolitan amphipod crustacean, Orchestia platensis, was examined at estuarine and open coastal habitats. Beach wrack was dominated by the plant genera Ascophyllum, Zostera, Spartina and Chondrus, and was most abundant during spring and late summer. Animal community numbers, biomass and frequency in fresh to moderately decomposed wrack were dominated by O. platensis throughout the year at all habitats; oligochaetes and Collembola were also important. The abundance of O. platensis showed high spatial and temporal variability, with low abundance generally associated with decreased amounts of wrack during colder months. An exception was the winter presence of the species at one estuarine habitat, in patchy aggregations within gravel-cobble refuges. The abundance of O. platensis averaged 1280 (0.04 m²)⁻¹, with a maximum of 7040 (0.04 m²)⁻¹. The life cycle of O. platensis is bivoltine, with summer-hatched young reaching maturity within 1 month. Laboratory studies indicate females with up to 4 broods (30 days)⁻¹, averaging 18 eggs brood⁻¹.Orchestia platensis is omnivorous, eating fresh plant tissue, live oligochaetes, Limulus eggs and diatom ‘fuzz’. The rate of laboratory consumption of algae and Zostera was 0.05 mg plant mg⁻¹ wet body weight day⁻¹. Presumptive predators of O. platensis are juvenile green crab, Carcinus maenus, and the earwig. Anisolabis maritima. The mobility, aggregation and aggressiveness of O. platensis assist the species in establishing and maintaining populations in the rigorous wrack habitat. The general competitive superiority of O. platensis over its congener, O. gammarella, and the co-occurrence of these species on both eastern and western Atlantic shores is discussed.  相似文献   

浅谈ARCGIS在国家1︰50000 DLG更新中的应用     

WU Yu-xian 《四川测绘》2008,(6)

通过分析ArcGIS中的ArcMap、ArcCatalog和ArcToolbox的特点,简要讨论了它们在国家1︰50000 DLG更新中的应用。  相似文献   

航空重力测量数学模型及其测量精度分析     

WANG Li-hong    ZHANG Chuan-ding  WANG Jun-qin  NIE Guo-xing 《测绘学院学报》2008,(1)

基于数学和分析力学角度分别推导了航空矢量重力测量的数学模型,得到了一致的模型公式;给出了矢量模型的3个分量形式,其中垂直方向的分量就是标量重力测量的数学模型;简要介绍了我国研制成功的航空标量重力测量系统CHAGS的数据处理的过程,分析了标量重力测量中测线交叉点和重复测线的重力异常的精度;根据实测数据计算的结果表明:测线交叉点重力异常不符值的标准差约为5×10-5ms-2左右,重复测线的内符合精度优于5×10-5ms-2,达到了预期的要求。  相似文献   

利用雷电定位系统进行电网雷击故障快速查询(英文)   总被引：1，自引：0，他引：1  

聂智平  赵文光  张萍  文银平  陈维江 《地球空间信息科学学报》2008,11(1):43-48

At present, lightning is one of the 10 natural disasters, and it is also the top environmental factor of power interruption. It often causes huge losses to the electric system. The Wuhan High Voltage Institute of the State Grid Corporation of China and Huazhong University of Science and Technology have been researching and developing lightning location systems （LLSs） since the late 1980s. In the mid-1990s, a lightning detection network was created in 29 provinces and cities in China. It is primarily applied to rapidly find lightning accidents, which greatly reduces power interruption. Also, it ensures high efficiency and safe operation of the electricity system. Remarkable benefit is achieved. China＇s LLS went through an ＂orientation positioning - time difference positioning - integrated positioning＂ development process. The positioning precision, detection efficiency, degree of automation, practicability and applied range are improved. Also, a lightning information system plan of the national network has been implemented, which services the whole society.  相似文献   

基于动态检测平台的GPS接收机动态性能检测研究     

任红飞  何峰  王若璞 《测绘信息与工程》2008,33(2):43-45

介绍了一种新型动态检测平台,设计了GPS动态差分试验和双动态差分试验,分析了GPS动态单点定位、动态差分测量、双动态差分测量在两种不同速度条件下进行了的试验数据.  相似文献   

GVG采样线代表性检验     

吴胜军  李涛  吴炳方  宋月君  冯奇 《遥感学报》2008,12(2):263-269

通过在实验区内设置不同类型的采样线,对GVG采样线的代表性进行检验.结果表明,高速公路和乡村道路类型的采样线对区域代表性的精度在95%以上;国道为86.726%;省道为65.447%.对于不同的缓冲区,高速公路、省道和乡村道路类型采样线,以200m缓冲区的代表性最好.而国道则以800m缓冲区的代表性最好.对于不同的作物而言,无论何种类型的采样线或者缓冲区,种植面积最大的棉花的精度是最好的.最低的是省道采样线1000m缓冲区,精度是78.146%,最好的是国道采样线800m缓冲区,精度是99.974%.除省道外,其他精度都在94.8%以上.这说明GVG采样线所获得的成数对于区域主要作物的代表性是很好的.  相似文献   

一种直线特征标志的子像素定位方法   总被引：1，自引：0，他引：1  

赵伶俐  刘帅  李俊生  傅锦伟 《测绘科学》2008,33(6):76-77,59

在近景摄影测量中,常常需要对直线特征的标志进行定位,而标志定位的精度会影响到整个测量的精度。不同特征的控制点标志,对应不同的识别方法,因此控制点标志的选择须根据不同的要求,进行综合研究分析。本文提出一种新的混合方法,首先采用Hough变换对直线特征标志进行直线检测,得到直线初值;然后采用灰度矩边缘直线拟合定位法,对标志点中心进行子像素定位。通过实验证明:经过Hough变换得到粗值的灰度矩边缘直线拟合定位法达到较高的定位精度,证明了该混合方法的有效性。  相似文献   

数字海洋地图无缝拼接的研究   总被引：1，自引：0，他引：1  

李晓欢  张雯  别红霞  李学明 《地理空间信息》2008,6(6):58-61

从目前数字海洋地图的现状出发,针对数字海洋地图由分幅存储方式带来的叠幅（图幅间存在重叠区域）和缝隙两个问题,提出了一种无缝拼接的算法。算法可去除图幅之间的重叠区域,并且可以有效去除由分幅导致的缝隙,将多个图幅的图层要素拼接为物理无缝的数据。  相似文献