An approximated method for the solution of elliptic problems in thin domains: Application to nonlinear internal waves     

A. Scotti  S. Mitran   《Ocean Modelling》2008,25(3-4):144-153

Realistic numerical simulations of nonlinear internal waves (NLIWs) have been hampered by the need to use computationally expensive nonhydrostatic models. In this paper, we show that the solution to the elliptic problem arising from the incompressibility condition can be successfully approximated by a few terms (three at most) of an expansion in powers of the ratio (horizontal grid spacing)/(total depth). For an n dimensional problem, each term in the expansion is the sum of a function that satisfies a one-dimensional second-order ODE in the vertical direction plus, depending on the surface boundary condition, the solution to an n-1 dimension elliptic problem, an evident saving over having to solve the original n-dimensional elliptic problem. This approximation provides the physically correct amount of dispersion necessary to counteract the nonlinear steepening tendency of NLIWs. Experiments with different types of NLIWs validate the approach. Unlike other methods, no ad hoc artificial dispersion needs to be introduced.  相似文献   

长距离网络RTK参考站间双差模糊度快速解算算法     

祝会忠  刘经南  唐卫明  高星伟 《武汉大学学报(信息科学版)》2012,37(6):688-692

提出了一种长距离网络RTK参考站间双差整周模糊度快速解算方法,该方法利用双频载波相位模糊度间的线性关系确定宽巷模糊度,然后选取双频载波相位的备选模糊度组合,通过计算参考站间对流层误差和轨道误差等非色散误差,对双频载波相位整周模糊度进行搜索。实验结果表明,此方法能够快速、可靠地解算长距离参考站间的双差整周模糊度。  相似文献   

利用语义的多版本网络覆盖服务模式匹配方法     

何杰  陈能成  郑重  王伟 《武汉大学学报(信息科学版)》2012,37(2):210-214

提出了一种基于节点相似度的语义模式匹配方法,首先对元素标签进行概念化,其次计算元素标签间的语义关系,再次计算节点概念并转化成合取范式CNF,最后利用命题可满足性问题解决器SAT验证节点间的概念关系。实验结果表明,该方法有效提高了匹配的查全率、精度和整体质量。  相似文献   

空间线群目标相似度计算模型研究   总被引：1，自引：0，他引：1  

刘涛  杜清运  毛海辰 《武汉大学学报(信息科学版)》2012,37(8):992-995

以空间线群目标的空间统计特征为基础,对线群目标的空间关系和几何特征进行了描述。利用拓扑关系概念邻域图定义线群之间的拓扑关系相似度,利用方向均值定义线群之间的方向关系相似度以及利用"环形方差"定义线群目标之间的距离相似度。结合线群的长度和平均长度、线群密度及线群曲折度,建立了线群目标相似度计算模型,对线群目标相似度进行了整体度量。实验结果表明,相似度计算结果与地物特征比较一致,符合人们的直观认知。  相似文献   

地籍信息与社会公共信息整合关系研究     

薛丰昌 《测绘与空间地理信息》2012,(5):8-9,13

采用文献资料法和比较分析法,建立了由"地籍空间分辨率圆锥"和"地籍时间参照系统"构成的区域地籍信息模型,阐述了现代地籍信息与社会公共信息整合关系在地籍空间定位系统、时间参照系统、边界系统及环境系统中的体现。  相似文献   

南京市土地利用效益耦合关系研究   总被引：2，自引：0，他引：2  

李冠英  张建新  刘培学  王小丹 《地域研究与开发》2012,31(1):130-134

土地利用效益的耦合程度是评价土地利用是否科学合理的依据之一,也是土地可持续利用研究的重要内容。在分析土地利用社会经济效益与生态环境效益耦合关系的基础上,借助系统科学理论与方法,建立南京市土地利用效益间的耦合模型和相应指标体系,利用1999—2009年的统计数据对南京市土地利用效益耦合度进行了研究。结果表明:(1)自1999年以来,南京市土地利用社会经济与生态环境效益都处于上升状态。(2)土地利用社会经济效益与生态环境效益的耦合度α一直处于19.16°～70.65°之间,即处于协调发展阶段。但近几年土地利用效益耦合度居高不下,土地利用效益之间的矛盾依然存在。  相似文献   

3mm多普勒云雷达测量反演云内空气垂直速度的研究   总被引：7，自引：4，他引：3  

彭亮  陈洪滨  李柏 《大气科学》2012,36(1):1-10

垂直指向的W-波段大气云雷达(WACR)不仅测量云粒子的反射率因子Z, 而且测量多普勒速度谱。本文利用寿县气象站WACR在2008年11月1日一个时段的测量, 进行云内空气垂直速度反演试验。首先讨论个例中反射率、 Doppler平均速度及谱宽的分布特征及原因, 然后利用小粒子示踪法和改进的以小粒子示踪法为基础的粒子下降速度w0—反射率因子 (w0－Z) 关系法反演了云内空气垂直速度, 进而结合Doppler谱数据分析反演结果。结果显示: 小粒子示踪法在湍流较弱时能比较精确地反演空气垂直速度, 而湍流较强时, 湍流造成的误差不可忽略; 改进算法在湍流较强时能够减少湍流对反演结果的影响。  相似文献   

Simulated Change in the Interannual Variability of South Asian Summer Monsoon in the 21st Century   总被引：1，自引：0，他引：1  

FU Yuanhai  LU Riyu 《大气科学进展》2010,27(5):992-1002

This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO-monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 (CMIP3) coupled models. The dynamical monsoon index (DMI) was adopted to describe the interannual variability of South Asian summer monsoon, and the standard dev...  相似文献   

Rainfall yield characteristics of electrical storm observed in the Spanish Basque Country area during the period 1992–1996     

A. Ezcurra  J. Saenz  G. Ibarra-Berastegi  J. Areitio 《Atmospheric Research》2008,89(3):233-242

This paper is focused on the study of rainfall yield characteristics of electrical storms observed over the Northern Iberian Peninsula during 1992–1996. To this aim Principal Components Analysis (PCA) and Self-Organizing Maps (SOM) method have been used. The SOM method is a group of artificial neural networks based on the topological properties of the human brain. Results clearly suggest that there exist three different meteorological patterns that are linked to the characteristics of electrical events found in the study area. In winter, most of the electrical events are formed under oceanic advection (NW air fluxes). On these cases, mean rainfall yield estimates reach values of 700 10⁴ m³ per cloud to ground lightning flash (CG flash). During summer most frequent electrical storms are associated to local instability shooting by surface heating with advection of humidity coming from the Iberian Peninsula. Under these meteorological situations, rain is scarcer if compared with oceanic events but lightning CG counts reach the maximum values found in the area (about 10 CG counts per 20 × 20 km² and day) giving this way the smallest rainfall yield with a mean value of 15 10⁴ m³ per CG flash. Iberian air fluxes associated with cold air in upper parts of the atmosphere represent the third meteorological pattern found. This pattern is most common in spring and autumn but is not unusual in the rest of the seasons. In those cases mean rainfall yield in the area is about 150 10⁴ m³ per CG flash. In all electrical episodes K instability index is greater than 15 °C but in the most lightning producing events, this index reaches in the area values greater than 24 °C. PCA results pointed out that there exists a relationship between rain and CG counts expressed by the first principal component computed from standardized data. However, we must notice that no event is solely linked to this axis, since a seasonal influence which decreases lightning production when rain increases is always present. Results found are of great interest for short term forecasting of flashfloods in mountainous areas like the Spanish Basque Country region.  相似文献   

Deduction of the Sensible Heat Flux from SODAR Data     

PAN Naixian  LI Chengcai 《大气科学进展》2008,25(2):253-266

A new method for deduction of the sensible heat flux is validated with three sets of published SODAR （sound detection and ranging） data. Although the related expressions have previously been confirmed by the author with surface layer data, they have not yet been validated with observations from the boundary layer before this work. In the study, selected SODAR data are used to test the method for the convective boundary layer. The sensible heat flux （SHF） retrieved from SODAR data is found to decrease linearly with height in the mixed layer. The surface sensible heat fluxes derived from the deduced sensible heat flux profiles under convective conditions agree well with those measured by the eddy correlation method. The characteristics of SHF profiles deduced from SODAR data in different places reflect the background meteorology and terrain. The upper part of the SHF profile （SHFP） for a complicated terrain is found to have a different slope from the lower part. It is suggested that the former reflects the advective characteristic of turbulence in upwind topography. A similarity relationship for the estimation of SHFP in a well mixed layer with surface SHF and zero-heat-flux layer height is presented.  相似文献