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61.
Past earthquakes, in many instances, have demonstrated poor performance of commonly used built-in staircase configurations. Codal provisions in India pertaining to staircases present a rather simple approach wherein the effects of built-in staircases on the overall dynamic properties or on the local behavior of structures are not addressed explicitly. Studies in the past have highlighted the scale of such effects, but most of them have relied completely on analytical models of buildings. This study analyzes the adequacy of the codal provisions by investigating two finite element (FE) models calibrated using ambient and forced vibration measurements. The effects of variations in building height, layout of staircase in plan, and presence of masonry infill walls in stairwells are also examined. The codal guidelines regarding empirical estimation of period and provision of enclosure walls around built-in staircases are found to be adequate. However, for the case of built-in staircases without enclosure walls, the force and displacement demands on landing beams are found to be considerably high. Drift-based approaches to estimate these demands are proposed. 相似文献
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引发暴雨天气的中尺度低涡的数值研究 总被引:1,自引:1,他引:0
2008年7月17—19日发生在山东的大到暴雨天气是由“海鸥”台风和副热带高压共同向山东输送水汽,与弱冷空气相互作用造成的。对流层低层的中尺度低涡是暴雨天气的直接制造者。利用常规观测资料和中尺度模式WRF(Weather Research and Forecasting)的模拟资料对该中尺度低涡的结构及形成机制进行了分析研究。结果表明,数值模拟可以清楚地捕捉到中尺度低涡东移过程中有新的涡旋中心形成,并与原来的涡旋中心合并的过程,而不是简单的沿切变线东移。中尺度低涡形成在增温增湿明显、上升运动为主的对流区内;中尺度低涡形成后其中心转为下沉运动,对流区东移,降水区位于低涡的东北和东南象限。中尺度低涡上空近地面层的冷池、600~400hPa的弱冷空气堆、900~850hPa的弱风区及高低空急流耦合发展是中尺度低涡形成和发展阶段的重要特征。中尺度低涡减弱阶段,下沉运动变强,低空急流和高空出流都明显减弱。涡度方程的收支表明,对流层低层的散度项、倾侧项及对流层中层的水平平流项和铅直输送项是正涡度的主要贡献者。中低层的水平辐合、涡度由低层向高层的垂直输送都有利于中尺度低涡的形成和发展。倾侧项对中尺度低涡的形成也有重要贡献。中尺度低涡形成后期,低层辐合、高层辐散及垂直输送的减弱导致正涡度制造的减弱,从而使中尺度低涡减弱。 相似文献
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根据台风自身的活动规律,利用逐步回归周期预后来研究台风的年活动强度,其结果是比较理想的,因而是进行台风长期及超长期预后的一条有效途径。 相似文献
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GRAPES模式对2005年登陆强台风预报检验分析 总被引:4,自引:1,他引:3
针对2005年4个登陆强台风,在台风移动路径、登陆时间、地点、强度等方面,对GRAPES模式的预报能力进行检验评价, 并进行了误差原因分析。检验结果显示,GRAPES 模式台风中心位置预报24 h平均误差131 km,48 h平均误差252 km。模式预报台风登陆的时间、地点接近实况,预报比较准确;台风登陆时的强度预报偏弱。模式48 h预报准确性略低于24 h。误差原因分析表明,需要加强对非常规观测资料的同化应用,改进模式初始条件;提高模式分辨率,使得模式对中小尺度系统的预报模拟能力增强;改进模式地形的精细处理方法,提高模式对地形影响涡旋移动的模拟能力。 相似文献
69.
The removal of noise and velocity ambiguity and retrieval and verification of horizontal wind
field is a prerequisite to make the best and fullest use of Doppler radar measurements. This approach was
applied to the Doppler radar data collected during August 2005 for a landing typhoon Matsa (0509) in
Yantai, Shangdong Province, and the verified result shows that the quality control for this dataset was
successful. The horizontal wind field was retrieved and then verified by studying the characteristics of the
radar radial velocity and large-scale wind field and the vertical cross section of the radial velocity
determined with the typhoon center as the circle center and comparing it with satellite imagery. The results
show that the meso- and small-scale systems in Matsa and its horizontal and vertical structure could be
clearly retrieved using the dataset collected by single Doppler radar, and a shear or a convergence was
corresponding with a band of severe storm around Matsa. At the same time, the retrieved wind field from
single Doppler radar is proved to be a reliable and high-resolution dataset in analyzing the inner
meso-scale structure of Matsa. It is also proved that the method for removing the velocity ambiguity could
be an effective approach for preliminary quality control of the Doppler radar data, and the VAP method
could also be a reasonable solution for the analysis of mesoscale wind field. 相似文献
70.
ASYMMETRIC DISTRIBUTION OF CONVECTION ASSOCIATED WITH TROPICAL CYCLONES MAKING LANDFALL ON THE EAST CHINA COAST 总被引:1,自引:1,他引:0
The asymmetric distribution of convection associated with tropical cyclones making landfall on the east China coast is studied with black-body temperature (TBB) data from Fengyun-2 (FY-2) geostationary weather satellite. The convection in various quadrants of the TCs is examined for the period of -24 to 6 h relative to landfall. The convection to the southern side of the TCs was much more intense than that to the northern side during the whole landfall period. The convection to the western side of the TCs was stronger than that to the eastern side for the time -8 h before and at the landfall. After landfall, the situation reverses. The asymmetric convection of the TCs was partly due to the vertical wind shear and storm motion, and partly because the process of landfall restrained the convection in relevant quadrants. Besides, the orographic uplift along the east of China was favorable to the enhancement of convection in the eastern side of the TCs. From the characteristics of convective asymmetry of the TCs landing on the south and east of China, it is known that their main difference might be the included angle between the TC path and the coastline as well as the terrain along the coast. 相似文献