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881.
Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration (VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation (LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters. 相似文献
882.
883.
通过对百色双套自动气象站遇到历史罕见的强雷暴袭击出现故障维修,摸索出了检修双套新型自动站的通信、电源供应、主机HY3000、接口RS232、分采仪器等模块的方法,供同行借鉴. 相似文献
884.
885.
基于GIS的广东冬种辣椒气候适宜性区划 总被引:3,自引:0,他引:3
基于广东省86个气象站1980-2012年气候资料和1991-2010年冬季寒害灾情资料,采用冬季(12月一翌年2月)≥15℃有效积温作为冬种辣椒的气候资源指标,选取寒害过程中最低气温<10℃的天数、日最低气温<10.0℃积寒量构建冬种辣椒的寒害风险指标,完善了冬种辣椒的种植气候适宜性指标.构建指标的空间分析模型,采用ArcGIS的空间分析和多层复合方法,对广东冬种辣椒的气候适宜性进行了区域划分.结果表明,冬种辣椒的气候最适宜种植区主要分布在雷州半岛、茂名、阳江等地区,适宜种植区主要分布在南部沿海地区和中部偏南地区,次适宜种植区主要分布在中部偏北地区和北部偏南地区,不适宜种植区主要分布在肇庆、清远、韶关、河源及梅州等地的北部. 相似文献
886.
2013年12月广西一次暴雨落区变化原因分析 总被引:1,自引:0,他引:1
利用micaps常规观测资料和NCEP再分析资料,对2013年12月13日~17日广西出现持续性强降雨天气的物理量场的分析得出:强降雨主要是由低层切变线和南支槽共同作用引起,各层天气系统对每天强降雨的贡献不尽相同,第一天高空南支槽还比较浅薄,强降雨主要由低层切变线和超低空东南急流引起;第二、第三天强降雨则是由加深东移的南支槽和北抬又南压的低层切变线共同作用引起;第四天降雨中低层转北风,只有500hPa南支槽和700hPa切变线共同影响. 相似文献
887.
Planktonic copepod Calanus sinicus is the dominant meso-zooplankton in the Northwest Pacific Ocean. To better understand its population dynamics and phylogeographic patterns, 243 C. sinicus individuals were collected from seven locations across the shelf waters of China and its population genetics was studied by mitochondrial DNA cytochrome oxidase I(mtCOI) sequences analyses. Thirty-nine different sequences, or haplotypes, were detected with moderate haplotype diversity(h=0.749) and low nucleotide diversity(π=0.003) for all populations. The evolutionary divergence between geographic populations varied from 0.24% to 0.37%, indicative of very limited genetic differentiation. Visualized minimum spanning network(MSN) and phylogenetic analysis of all the detected haplotypes did not reveal any clear phylogeographic pattern. Furthermore, AMOVA data showed no significant spatial population differentiation existed among the individuals collected across China shelf waters. Pairwise FST values showed that population collected from northwest of the East China Sea(ECS) displayed a low difference to other populations. Mismatch distribution analyses and neutrality tests indicated that C. sinicus might undergo a demographic/population expansion. No significant population genetic structuring was detected, indicating an extensive gene flow among the C. sinicus populations. Our results provide molecular evidence for the hypothesis that C. sinicus in the northwestern South China Sea in winter is transported from the East China Sea and the Yellow Sea by the China Coastal Current during the northeast monsoon period. 相似文献
888.
HUANG Wenyu WANG Bin LI Lijuan DONG Li LIN Pengfei YU Yongqiang ZHOU Tianjun LIU Li XU Shiming XIA Kun PU Ye WANG Lu LIU Mimi SHEN Si HU Ning WANG Yong SUN Wenqi DONG Fang 《大气科学进展》2014,31(1):95-109
The variability of Atlantic Meridional Overturning Circulation (AMOC) in the pre-industrial control experiment of the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2) was investigated using the model outputs with the most stable state in a 512-yr time window from the total 1500-yr period of the experiment. The period of AMOC in FGOALS-g2 is double peaked at 20 and 32 years according to the power spectrum, and 22 years according to an auto-correlation analysis, which shows very obvious decadal variability. Like many other coupled climate models, the decadal variability of AMOC in FGOALS-g2 is closely related to the convection that occurs in the Labrador Sea region. Deep convection in the Labrador Sea in FGOALS-g2 leads the AMOC maximum by 3-4 years. The contributions of thermal and haline effects to the variability of the convection in three different regions [the Labrador, Irminger and Greenland-Iceland- Norwegian (GIN) Seas] were analyzed for FGOALS-g2. The variability of convection in the Labrador and Irminger Seas is thermally dominant, while that in the colder GIN Seas can be mainly attributed to salinity changes due to the lower thermal expansion. By comparing the simulation results from FGOALS-g2 and 11 other models, it was found that AMOC variability can be attributed to salinity changes for longer periods (longer than 35 years) and to temperature changes for shorter periods. 相似文献
889.
Improvement of the semi-Lagrangian advection scheme in the GRAPES model: Theoretical analysis and idealized tests 总被引:2,自引:0,他引:2
ABSTRACT The Global/Regional Assimilation and PrEdiction System (GRAPES) is the newgeneration numerical weather predic- tion (NWP) system developed by the China Meteorological Administration. It is a fully compressible non-hydrostatical global/regional unified model that uses a traditional semi-Lagrangian advection scheme with cubic Lagrangian interpola tion (referred to as the SL_CL scheme). The SL_CL scheme has been used in many operational NWP models, but there are still some deficiencies, such as the damping effects due to the interpolation and the relatively low accuracy. Based on Reich's semi-Lagrangian advection scheme (referred to as the R2007 scheme), the Re_R2007 scheme that uses the low- and high-order B-spline function for interpolation at the departure point, is developed in this paper. One- and two-dimensional idealized tests in the rectangular coordinate system with uniform grid cells were conducted to compare the Re..R2007 scheme and the SL_CL scheme. The numerical results showed that: (1) the damping effects were remarkably reduced with the Re_R2007 scheme; and (2) the normalized errors of the Re_R2007 scheme were about 7.5 and 3 times smaller than those of the SL_CL scheme in one- and two-dimensional tests, respectively, indicating the higher accuracy of the Re..R2007 scheme. Furthermore, two solid-body rotation tests were conducted in the latitude-longitude spherical coordinate system with non uniform grid cells, which also verified the Re_R2007 scheme's advantages. Finally, in comparison with other global advection schemes, the Re_R2007 scheme was competitive in terms of accuracy and flow independence. An encouraging possibility for the application of the Re_R2007 scheme to the GRAPES model is provided. 相似文献
890.
The impact of asymmetric thermal forcing associated with land–sea distribution on interdecadal variation in large-scale circulation and blocking was investigated using observations and the coupled model intercomparison project outputs. A land–sea index (LSI) was defined to measure asymmetric zonal thermal forcing; the index changed from a negative to a positive anomaly in the 1980s. In the positive phase of the LSI, the 500 hPa geopotential height decreased in the polar regions and increased in the mid-latitudes. The tropospheric planetary wave activity also became weaker and exerted less easterly forcing on the westerly wind. These circulation changes were favorable for westerly wind acceleration and reduced blocking. In the Atlantic, the duration of blocking decreased by 38 % during the positive LSI phase compared with that during the negative phase; in Europe, the number of blocking persisting for longer than 10 days during the positive LSI phase was only half of the number during the negative phase. The observed surface air temperature anomaly followed a distinctive “cold ocean/warm land” (COWL) pattern, which provided an environment that reduced, or destroyed, the resonance forcing of topography and was unfavorable for the development and persistence of blocking. In turn, the responses of the westerly and blocking could further enhance continental warming, which would strengthen the “cold ocean/warm land” pattern. This positive feedback amplified regional warming in the context of overall global warming. 相似文献