Groundwater modelling: Towards an estimation of the acceleration factors of iterative methods via an analysis of the transmissivity spatial variability     

Abdelmajid Benali 《Comptes Rendus Geoscience》2013,345(1):36-46

When running a groundwater flow model, a recurrent and seemingly subsidiary question arises at the starting step of computations: what value of acceleration parameter do we need to optimize the numerical solver? A method is proposed to provide a practical estimate of the optimal acceleration parameter via a geostatistical analysis of the spatial variability of the logarithm of the transmissivity field Y. The background of the approach is illustrated on the successive over-relaxation method (SOR) used, either as a stand-alone solver, or as a symmetric preconditioner (SSOR) to the gradient conjugate method, or as a smoother in multigrid methods. It shows that this optimum acceleration factor is a function of the standard deviation and the correlation length of Y. This provides an easy-to-use heuristic procedure to estimate the acceleration factors, which could even be incorporated in the software package. A case study illustrates the steps needed to perform this estimation.  相似文献   

一次持续性大雾边界层结构特征及诊断分析   总被引：2，自引：0，他引：2  

马翠平  吴彬贵  李江波  于雷  赵娜  蔡子颖  曲晓黎 《气象》2014,40(6):715-722

2010年11月30日至12月2日,冀中南部及天津地区出现了一次大范围的大雾天气,持续时间长达3 d,其中石家庄浓雾持续时间长达34 h,强浓雾持续时间7 h。利用加密自动站、天津市250 m气象铁塔梯度观测资料,结合常规气象资料和NCEP/NCAR再分析资料,对连续性大雾边界层结构特征以及大雾的形成、发展维持和消散进行了诊断分析。研究得到:大雾形成前期地面持续东风,有利水汽的聚积;当地面风向转为偏北风时促进水汽凝结,致使大雾形成,大雾形成后再次转为长时间偏东风有利大雾的维持和加强;850 hPa以下西南暖湿气流和近地面层逆温的长时间维持,是平流大雾持续的主要原因;低层3支水汽的输送及850 hPa的西南急流重建直接导致了强浓雾形成。大雾维持加强期间,边界层风速为1~2 m·s~(-1),尤其是强浓雾期间,风速仅为1 m·s~(-1);当边界层4 m·s~(-1)以上西北风速从250 m逐渐下传至地面时,逆温层破坏,大雾天气结束。  相似文献   

Re-Envisioning the City: Lefebvre,HOPE VI,and the Neoliberalization of Urban Space     

《Urban geography》2013,34(1):114-133

This study draws upon the urban theory of Henri Lefebvre to examine HOPE VI, a public housing demolition and redevelopment program administered by the U.S. Department of Housing and Urban Development. Hailed as a new approach to urban policy, the HOPE VI program embodies many of the key tenets of neoliberal urbanization, including an emphasis on entrepreneurial forms of urban regeneration and a focus on individual responsibility. To provide a lens for understanding this neoliberalization of space, we first detail Lefebvre's theorization of abstract space and transparency, highlighting in particular its nondialectical and depoliticized character. We then turn to examine the HOPE VI model and its implementation in Charlotte, North Carolina. Lefebvre's analysis, we argue, provides a useful entry point for interpreting the re-envisioning of urban space that underlies HOPE VI-style redevelopment, and therefore can potentially inform contemporary struggles against neoliberal urban policy.  相似文献   

松花江汛期最高水位预报     

袁美英  潘华盛  张桂华  董淑华 《黑龙江气象》2001,(3):9-11,15

利用人工神经网络和逐步回归方法对松花江汛期最高水位进行模拟，并对1996、1997、1998年的最高水位进行了试报，效果极佳。试报1998年松花江最高水位119．69m，实况120．89m，仅差1．2m；报出大洪水；而且在1999、2000年业务预报中也准确报出松花江出现的枯水位。两种方法可以在实际中推广应用。  相似文献   

Seasonal and interannual variations in pigments in the Adriatic Sea     

Mira MoroviĆ 《Journal of Earth System Science》2002,111(3):215-225

Spatial and temporal variability of pigments was studied from the CZCS satellite data and fromin situ chlorophyll and transparency for the period 1979-1985. The three Adriatic sites, Northern, Middle, and Southern Adriatic are differently influenced by meteorological, hydrological and oceanographic parameters. The differences between seasonalin situ chlorophyll and remotely sensed pigment concentrations (from CZCS satellite data) from the Adriatic are large in winter. Through the correlation analysis, pigments were compared to meteo-oceanographic and hydrological parameters from different Adriatic sites. The PCA (principal component analysis) was applied to the pigment data series and significant components were compared. Different correlations are obtained for warm and cold periods of the year pointing to seasonal differences in the underlying mechanism of pigment variability. The first PC is influenced mainly by temperature. In the warm period more parameters seem to influence the pigment field, than in the cold period. The pigments in the Adriatic are in good correlation to a number of hydrologic and meteo-oceanographic factors.  相似文献   

'On Solving Kepler's Equation For Nearly Rectilinear Hyperbolic Orbits'     

Richard A. Serafin 《Celestial Mechanics and Dynamical Astronomy》2002,82(4):363-373

We deal here with efficient starting points for Kepler's equation in a special case of nearly rectilinear hyperbolic orbits, that is these ones with the eccentricities e1. These orbits appear in stellar dynamics when considering encounters of stars. We test efficiency of these starters for the method for successive approximation (MSA) in its two often applied variants, that is the Newton's method with the quadratic convergence (NM) and in the fixed point method (FPM). Moreover, we determine a dynamical domain of Kepler's equation for this motion.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

GDI+在电子地图可视化中的应用   总被引：4，自引：1，他引：3  

车森  刘海砚  刘辉  兰梅 《测绘科学》2008,33(1):226-228

电子地图显示的美观和效率一直是设计者和用户不断追求的目标,目前电子地图的开发中普遍还是应用GDI进行图形的显示,但是GDI对电子地图显示的美观性、显示效率存在着一定的制约。GDI+作为GDI的升级版本,功能有了较大改善,针对GDI+的新特色,论文详细介绍了GDI+在电子地图可视化中的应用。实践证明,GDI+对于电子地图绘图效率的提高、显示效果的改善以及变形字体的显示,都有较好的效果。  相似文献   

海洋水团的Fisher型逐步判别预报     

李凤岐  苏育嵩 《中国海洋大学学报(自然科学版)》1989,(Z1)

判别分析是多元分析方法之一,我们将其应用于海洋水团的判别预报。用逐步判别的方法挑选因子,依每个因子的Wilks量进行F—检验,逐步地将判别“能力”强的因子选入。同时将由于其他因子组合而相形见绌者及时剔除。根据矩阵变换的信息,给出了Fisher型逐步判别预报式。将北黄海冷水团强度预报作为示例,给出了筛选因子及建立判别式的全过程。用历史资料检验了预报效果。与习用的Bayes型逐步判别预报进行了对比。  相似文献   

Long-term study of heterotrophic bacteria as indicators of eutrophication of the open middle adriatic sea     

《Estuarine, Coastal and Shelf Science》1990,30(6)

Results of the 20-year study, from 1968 to 1988, indicate a trend of increasing density of heterotrophic bacteria in the open middle Adriatic Sea. An identical trend has been observed for primary production resulting in an increase of oxygen saturation in the layer of maximum primary production. Transparency of seawater decreased during the investigated period.This suggests that fluctuations of hydrographic, chemical and biological parameters in the open middle Adriatic Sea are not only a result of the influence of natural factors but are influenced by coastal eutrophication as well. Eutrophication rapidly extended towards the open Adriatic Sea after the late 1970s.  相似文献   

基于GF-1影像的洞庭湖区水体水质遥感监测   总被引：1，自引：0，他引：1  

彭保发  陈哲夫  李建辉  罗望军  甘洁  曾荣亮 《地理研究》2018,37(9):1683-1691

湖泊水质监测是有效开展湖泊水环境综合管理与水污染防治实施的基础,也是湖泊藻华风险评估与生态安全建设的重要依据。本文基于GF-1号影像对2014-2016年洞庭湖水体的叶绿素a浓度、悬浮物浓度和透明度展开遥感监测,结果表明：叶绿素a主要集中在水流速度较慢的安乐湖、大小西湖和东洞庭湖西部地区,其他区域水体扰动力大,叶绿素含量a较低。透明度从北到南递增,与悬浮物浓度的分布趋势相反,符合常规监测规律。东洞庭湖水质较南洞庭湖和西洞庭湖差,水污染程度处于全湖最高水平。GF-1数据可精确反映叶绿素a浓度、悬浮物浓度和透明度指数的空间变化规律,也为后续高分遥感影像湖泊水质监测的应用研究提供了重要参考。  相似文献