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991.
A generalization of the TOPMODEL equations for a power law vertical profile of hydraulic conductivity is introduced. The exponential profile of TOPMODEL is obtained as a limit case of the new general form. © 1997 John Wiley & Sons, Ltd. 相似文献
992.
Field observations on hydraulics and sediment dynamics during extreme floods in two mountain torrents show the influence of man-made constructions such as bridges and check dams, in addition to the sediment supplied naturally by the basin and the channel network, on the formation of hyperconcentrated flows. In the Pyrenean Arás basin, hyperconcentrated flow occurred after collapse of a bridge, which in turn mobilized large volumes of sediment from the stream channel and, subsequently, destroyed a series of check dams. Boulders up to several metres in size were transported in a mixture of sand and fine material. A minimum of 100000 tonnes of sediment were deposited on the alluvial fan during the event. Prior to bridge destruction, mean bedload transport rates had reached 0.4t m−1 s−1 upstream. In the alpine Lainbach basin, the flood was characterized by transportation of large amounts of slope material, including debris flows. Along its main tributary an intensive hyperconcentrated flow occurred during the rising stage, whereas in the main valley smaller flows occurred after failure of check dams. The depth of coarse material deposited reached 80 cm. The effectiveness of the Aràs and Lainbach floods was attained due to exceptional rates of energy expediture. Flood power ranged from 20000 W m−2 to 40000 W m−2 on average. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
993.
Elastic closed-form solutions for the displacements and stresses in a transversely isotropic half-space subjected to various buried loading types are presented. The loading types include finite line loads and asymmetric loads (such as uniform and linearly varying rectangular loads, or trapezoidal loads). The planes of transverse isotropy are assumed to be parallel to its horizontal surface. These solutions are directly obtained from integrating the point load solutions in a transversely isotropic half-space, which were derived using the principle of superposition, Fourier and Hankel transformation techniques. The solutions for the displacements and stresses in transversely isotropic half-spaces subjected to linearly variable loads on a rectangular region are never mentioned in literature. These exact solutions indicate that the displacements and stresses are influenced by several factors, such as the buried depth, the loading types, and the degree and type of rock anisotropy. Two illustrative examples, a vertical uniform and a vertical linearly varying rectangular load acting on the surface of transversely isotropic rock masses, are presented to show the effect of various parameters on the vertical surface displacement and vertical stress. The results indicate that the displacement and stress distributions accounted for rock anisotropy are quite different for those calculated from isotropic solutions. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
994.
2012年7月下旬河套地区4次切变暴雨的对比分析 总被引:1,自引:0,他引:1
应用日常预报业务中可以方便使用的常规观测资料、数值预报产品、卫星云图、加密自动站观测资料以及雷达资料等,从环流背景、流型配置、物理机制等方面对比分析了河套地区4次暴雨过程,旨在提高对暴雨的短期预报预测能力及短时强降水的临近预警能力。分析发现:(1)副热带高压西侧的偏南气流以及来自孟加拉湾的暖湿偏南气流在35°—40°N与来自高纬度的干冷的偏北气流多次交汇,水汽在该带中明显辐合,为河套地区持续性暴雨发生发展提供源源不断的水汽,提供水汽辐合上升动力条件;(2)暴雨落区与低层的显著流线出口区或急流出口区的位置、切变线的位置密切相关,暴雨一般落在高空急流的右侧、低空急流的左侧;(3)暴雨天气出现前一般会出现500 hPa以下θ随高度的增加而减少的特征;(4)暴雨天气出现前一般都会出现风随高度顺转的特征;(5)暴雨过程中地面辐合线起到动力抬升作用,触发中小尺度系统的生成和发展;(6)抬升凝结高度和自由对流高度都比较低,利于水汽凝结,而平衡高度较高,利于能量的积累,对于对流天气的预报有较好的指示意义。 相似文献
995.
A generalized flux law, which can specialize into power‐ and diffusive‐type flux laws, is proposed. When coupled with the continuity equation, a generalized flow equation is the result. The generalized equation specializes into several cases, one of which is the kinematic wave equation. By applying the generalized flow equation and its variants to flow routing in two rivers, the usefulness of the generalized flux law is evaluated. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
996.
On the basis of NOAA/CPC data of sea surface temperature anomaly in the Nino regions during Jan. 1950 - Dec. 2003, the wavelet power spectrum of SST were studied with significance and confidence testing at different scales in this paper. It shows that the SST are provided with multi-time scales structure nested one another, and vary on scales of 2 - 7 years, 8 - 20 years and >30 years. The most significant variation of the warm and cold episodes is in the 4-year band of period. The power, frequency structure and confidence of the same episode are different in different Nino regions. The intensity of oscillations is increasing at low frequency bands and decreasing at high frequency bands from east to west in the Nino regions, especially after 1970. 相似文献
997.
遥感在滩涂演变调查中的应用方法研究 总被引:5,自引:2,他引:5
本文主要介绍一种在潮滩演变遥感调查中确定任意潮位线的方法,该方法主要包括根据遥感图像上实时水边线的位置,结合收集到的水边线高程数据和另一潮位的高程数据,用图解法或计算法求取任意潮位线修正量,以确定所求潮位线的位置等内容。该方法在海南洋浦地区滩涂演变调查中使用后效果较好。 相似文献
998.
999.
在利用普通克里金方法外推的基础上,通过频域径向平均功率谱估算噪声方差,采用迭代维纳滤波法获取较为稳定的重力场向下延拓结果,并分别利用模拟算例和实际数据进行实验。对于模拟算例,外推后的均方根误差由6.72 μGal下降到1.89 μGal,相对误差由9.26%下降到4.44%。对于实际数据,外推后延拓结果不仅可避免边缘失真现象,而且能更好地反映浅源高频异常特征信息。 相似文献
1000.
车道线是自动驾驶高精度地图的组成部分,利用车载摄像头和激光雷达提取车道线的研究已经比较深入。本文探讨了利用高分辨率遥感影像提取车道线的方法。首先依据直方图原则选取合适的阈值进行二值化分割,其次利用道路中线形成的缓冲区去除道路范围外的要素,然后利用形态学算子去除噪声,最后利用方向和面积因子提取不同的车道线。该方法可以降低数据采集的成本,提高采集效率。 相似文献