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排序方式: 共有671条查询结果,搜索用时 46 毫秒
101.
为建立适用于遥感相机定标的实验室,需要有几何标定的算法和软件对摄影图像进行计算.使用近景摄影测量中基于3维控制场的定标方法,对单CCD四波段遥感相机进行了几何定标,研究并自主编程实现了直接线性变换DLT(Direct Linear Transformation)算法,与基于空间后方交会算法的定标结果进行了精度对比.结论... 相似文献
102.
Efficient conceptual model for simulating the effect of aquifer heterogeneity on natural groundwater discharge to rivers 总被引:1,自引:0,他引:1
David Pulido-Velazquez Carlos Llopis-Albert Salvador Peña-Haro Manuel Pulido-Velazquez 《Advances in water resources》2011,34(11):1377-1389
When linearity can be assumed (linear response of heads to stresses), stream–aquifer flow exchange can be simulated as the drainage of a number of independent linear reservoirs. This conceptual model, which can be mathematically deduced in a univocal way from an eigenvalue solution of the linear groundwater flow problem, facilitates the understanding of the physical phenomenon and the analysis of influencing factors. The number of reservoirs required to simulate stream depletion in some ideal homogeneous cases of stream–aquifer connection was analyzed in detail in a previous investigation using analytical eigenvalue solutions [16]. However, most aquifers are heterogeneous in nature and numerical solutions must be employed to analyze whether they could also be simulated using few reservoirs. This paper presents a stochastic analysis of the influence of heterogeneity on the simulation of natural groundwater discharges in aquifers connected to rivers, as a series of linear reservoirs. A Monte-Carlo approach was employed to perform this study. The results show that, on a monthly time scale, many cases (even heterogeneous aquifers) can be simulated using just a few reservoirs with sufficient accuracy and at minimum computational cost. Therefore, this modeling technique can be useful to efficiently simulate the integrated management of complex water resources systems at the basin scale (with many aquifers, reservoirs, demands, etc.) that need to simultaneously consider surface and groundwater flow and stream–aquifer interaction. 相似文献
103.
Alessandro Valiani Valerio Caleffi 《Advances in water resources》2011,34(2):227-242
This paper addresses the integral conservation of linear and angular momentum in the steady hydraulic jump in a linearly diverging channel.The flow is considered to be divided into a mainstream that conveys the total liquid discharge, and a roller where no average mass transport occurs. It is assumed that no macroscopic rheological relationship holds, so mass, momentum and angular momentum integral balances are independent relationships. Normal stresses are assumed to be hydrostatic on vertical, cylindrical surfaces. Viscous stresses are assumed to be negligible with respect to turbulent stresses. Assuming that the horizontal velocity distribution in the mainstream is uniform and that the horizontal momentum and angular momentum in the roller are negligible with respect to their mainstream counterparts, an analytical solution is obtained for the free surface profile of the flow. This solution is fundamental for finding the sequent depths and their positions. Consequently, it permits solving for the length of the jump, which is assumed to be equal to the length of the roller. Mainstream and roller thicknesses can also be derived from the present solution. This model may also be theoretically used to derive the average shear stresses exerted by the roller on the mainstream and the power losses per unit weight. This second relationship, which returns the well-known classical expression for total power loss in the jump, demonstrates that the strongly idealized mechanical model proposed here is internally consistent. 相似文献
104.
105.
为克服现有圆填充算法效率低的缺点,提出一种快速圆填充算法。算法基于圆的对称性,利用圆弧离散轨迹所具有的特性,分别绘制半径由0依次增加一个像素点,直到变为给定半径r的多个圆,同时找出并填充其中的漏点。最后达到快速填充整个圆的效果。 相似文献
106.
107.
主要分析了1951~2004年夏季亚洲极涡强度和面积的长期变化趋势及其对东亚夏季环流,水汽输送和降水量的影响,发现1951~2004年,夏季亚洲极涡表现出了明显的强度减弱,面积缩小的变化趋势,并以面积缩小更为显著,这正对应于北极涛动(AO)指数在该时段的显著升高.在这种北半球中高纬大尺度环流变化的影响下,东亚夏季高空西风急流在近54年显著南移,冷空气活动的南侵程度明显增强,从而造成低空偏北风显著增强而偏南风减弱.与此相应,近54年整个中国区域内低空纬向风速呈明显的减小趋势.总的来看,东亚夏季风环流发生了明显减弱.同时,流经中国的中纬度西风水汽输送在近54年也表现出一致减弱的趋势,而南风水汽输送大致以110°E为界,以东的夏季风区呈显著的减弱趋势而以西则有明显的增加趋势.这种水汽输送的变化影响了中国不同区域内水汽输送通量散度的改变,进而使得夏季降水量发生变化.分析表明,夏季亚洲极涡的面积和强度与东北、华北和西北东部的水汽输送通量散度和夏季降水呈正相关,而与长江中下游、华南、西南、青藏高原和西北西部呈显著负相关,夏季亚洲极涡在近几十年的面积缩小和强度减弱是中国夏季降水长期变化的一个可能原因. 相似文献
108.
Nien-Sheng Hsu Wei-Chen Cheng Wen-Ming Cheng Chih-Chiang Wei William W.-G. Yeh 《Advances in water resources》2008
This paper develops an iterative procedure for capacity expansion studies for water distribution systems. We propose a methodology to analyze an existing water distribution system and identify the potential bottlenecks in the system. Based on the results, capacity expansion alternatives are proposed and evaluated for improving the efficiency of water supply. The methodology includes a network flow based optimization model, four evaluation indices, and a series of evaluation steps. We first use a directed graph to configure the water distribution system into a network. The network flow based model optimizes the water distribution in the system so that different expansion alternatives can be evaluated on a comparable basis. This model lends itself to linear programming (LP) and can be easily solved by a standard LP code. The results from the evaluation tool help to identify the bottlenecks in the water distribution system and provide capacity expansion alternatives. A useful complementary tool for decision making is composed of a series of evaluation steps with the bottleneck findings, capacity expansion alternatives, and the evaluation of results. We apply the proposed methodology to the Tou-Qian River Basin, located in the northern region of Taiwan, to demonstrate its applicability in optimization and capacity expansion studies. 相似文献
109.
Yury V. Fedorenko Tatiana Matveeva Elena Beketova Eystein S. Husebye 《Physics of the Earth and Planetary Interiors》2008,168(3-4):231-236
A long-standing problem in operational seismology is that of reliable focal depth estimation. Standard analyst practice is to pick and identify a ‘phase’ in the P-coda. This picking will always produce a depth estimate but without any validation it cannot be trusted. In this article we ‘hunt’ for standard depth phases like pP, sP and/or PmP but unlike the analyst we use Bayes statistics for classifying the probability that polarization characteristics of pickings belong to one of the mentioned depth phases given preliminary epicenter information. In this regard we describe a general-purpose PC implementation of the Bayesian methodology that can deal with complex nonlinear models in a flexible way. The models are represented by a data-flow diagram that may be manipulated by the analyst through a graphical-programming environment. An analytic signal representation is used with the imaginary part being the Hilbert transform of the signal itself. The pickings are in terms of a plot of posterior probabilities as a function of time for pP, Sp or PmP being within the presumed azimuth and incident angle sectors for given preliminary epicenter locations. We have tested this novel focal depth estimation procedure on explosion and earthquake recordings from Cossack Ranger II stations in Karelia, NW Russia, and with encouraging results. For example, pickings deviating more than 5° off ‘true’ azimuth are rejected while Pn-incident angle estimate exhibit considerable scatter. A comprehensive test of our approach is not quite easy as recordings from so-called Ground Truth events are elusive. 相似文献
110.
Qiang Zhang Chong-Yu Xu Zengxin Zhang Yongqin David Chen 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(6):721-735
The spatial and temporal patterns of the temperature extremes defined by 5th and 95th percentiles based on daily maximum/minimum
temperature dataset were analyzed using Mann–Kendall test and linear regression method. The research results indicate that:
(1) the seasonal minimum temperature is in stronger increasing trend than the seasonal maximum temperature; (2) in comparison
with the changes of the maximum temperature, more stations display significantly increasing trends of minimum temperature
in frequency and intensity; (3) comparatively, more stations have significantly decreasing trends in the intra-seasonal extreme
temperature anomaly in summer and winter than in spring and autumn. The areal mean minimum temperature is in stronger increasing
trend than areal mean maximum temperature; (4) the warming process in the Far-West (FW) China is characterized mainly by significantly
increasing minimum temperature. The research will be helpful for local human mitigation to alterations in water resource and
ecological environment in FW China due to changes of temperature extremes, as the ecologically fragile region of China. 相似文献