柔性尾鳍推进装置的机构综合与优化设计   总被引：1，自引：0，他引：1  

陈先国  向忠祥 《海洋技术学报》1997,16(3):32-37

根据柔性尾鳍推进装置所需达到的性能特性要求，本文对该装置进行了机构综合与优化设计，以改善其水动力性能，提高其推进效率。  相似文献   

气候变化情景下泥石流危险性响应分析     

徐粒  李倩  王瑛  黄靖玲  许映军 《气候变化研究进展》2020,16(4):415-423

通过中国1950—2010年降水日值0.5°×0.5°格点数据和CMIP5的6个气候模式数据,以2010年舟曲8·7特大山洪泥石流为例,估算此次灾害发生的降雨重现期,并估算未来同等重现期下的降雨量,基于HEC-HMS和FLO-2D模型模拟该降雨量下山洪泥石流堆积面积与泥沙冲出量,进而得到了气候变化背景下的泥石流危险性变化。结果表明：2010年舟曲8·7山洪泥石流灾害的降雨重现期为1500 a,未来相同重现期下降雨量为113.7 mm。设防水平不变条件下,舟曲县城泥石流堆积面积可达2010年灾害的173%,总泥沙量增加到148%,且泥石流堆积面积增加的区域主要位于2010年舟曲县城人口密集区。可见,灾后重建中舟曲县城一半以上居民的转移安置政策有利于弱化未来气候变化背景下泥石流危险性增加的不利影响,是一种有效的气候变化适应性举措。  相似文献   

基于闪电定位系统的雷击建筑物绕击率分析与区划     

李家启 《气象科技》2013,41(2):412-416

通过对重庆地区1999-2008年闪电定位系统监测地闪资料进行数理统计,重点对采用IEEE和DL/T620提供的公式获取的雷击建筑物绕击率进行对比分析,并对重庆全市进行雷击建筑物绕击率区划.结果表明:雷击建筑物绕击率随着滚球半径增大而增加;对于相同滚球半径,IEEE方法获取的雷击建筑物绕击率略高于实际,而低于GB/T21714提供的绕击率;在滚球半径小于120 m时,IEEE方法得到绕击率明显低于DL/T620方法,反之则高于DL/T620方法;采用IEEE公式获取的雷击建筑物绕击率与实际较为吻合,在此基础上获得了能客观反映重庆地区雷击建筑物绕击率表达式,并对不同防雷类别建筑物雷击绕击率进行了区划,为雷电灾害风险评估和防雷设计提供了可靠理论依据.  相似文献   

Influence of the Return Current on the EUV and X-Ray Flare Line Emissions     

Elena Dzifčáková  Marian Karlický 《Solar physics》2008,250(2):329-338

Electron beams accelerated during solar flares carry electric currents which should be neutralized by so-called return currents. Both the electron beam and return current modify the electron distribution function in the solar transition region and low corona. Thus, they influence the intensities of the spectral lines formed in these layers. Synthetic spectra for the solar flare atmosphere are computed from model conditions and the possibilities of diagnostics of the return current from the EUV and X-ray line spectra are discussed.  相似文献   

气象因素与中暑发生关系的探讨   总被引：7，自引：2，他引：7  

王长来  茅志成  程极壮 《气候与环境研究》1999,4(1):40-43

对1988、1994、1995年3个高温年份南京市区260万自然人群中563例重症中暑病例与逐日气象因素作了多元逐步回归分析。以发病当日平均气温x1、最高气温x2、相对湿度x3、平均风速x4、日照时间x5和降水量x6等6个气象因素以及这些因素与发病前1～5天的2～6天平均值M11~M15、……、M61~M65共36项因素作为自变量;以重症中暑总例数作为应变量。筛选结果：x1、x3、M12、M32四项对Y有显著贡献。由标准回归系数可见,x1较x3,M12较M32贡献大。连续3日的平均气温M12及相对湿度M32较 x1、x3对日重症中暑人数影响要大。当M12超过30oC且M32超过73%易出现中暑。这结果在1997年做了初步应用验证。  相似文献   

Sea level extremes in Marseille (NW Mediterranean) during 1885–2008     

Camille Letetrel  Marta Marcos  Belén Martín Míguez  Guy Woppelmann 《Continental Shelf Research》2010

Sea level extremes and their temporal variability have been explored based on the hourly measurements at Marseille tide gauge for the period 1885–2008. A careful quality check has first been applied to the observations to ensure consistency of the record by eliminating outliers and datum shifts. Yearly percentiles have been used to investigate long-term trends of extremes revealing that secular variations in extremes are linked to mean sea level changes. The associated decadal changes show discrepancies between mean sea level trend and extreme fluctuations, due to the influence of the atmospheric forcing. A local regression model based on the generalized Pareto distribution has been applied to derive trends in return levels. The 50-years return levels reach values between 80 and 120 cm. The most significant changes in return levels are characterized by an increase since the 1970s.  相似文献   

木星极光区亮斑形成机制   总被引：1，自引：1，他引：0       下载免费PDF全文

卢斌  陈出新 《地球物理学报》2010,53(11):2544-2550

近年来一系列的木星照片显示,除了主极光卵和卫星足迹外,在极光卵内还有极区发射.学者基本认为这是由中磁尾的磁场活动引起的.本文建立一个具有离心力效应的木星稳态磁场模型.并以该模型给出的磁场结果为基础,利用Hill等人1979年总结的木星磁层较差自转的结果进行模拟分析.结果显示在约54R_j (R_j为木星平均半径) 至60R_j的木星磁场由于较差自转形成涡旋结构,其形状约为5R_j的圆形.由于磁力线的扭曲引发大小为数十万安培的电流注入极区电离层,与中性粒子相互作用,从而形成极光卵内的亮斑.  相似文献   

Bayesian stochastic modelling for avalanche predetermination: from a general system framework to return period computations   总被引：1，自引：1，他引：0  

N. Eckert  E. Parent  M. Naaim  D. Richard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):185-206

Stochastic models are recent but unavoidable tools for snow avalanche hazard mapping that can be described in a general system framework. For the computation of design return periods, magnitude and frequency have to be evaluated. The magnitude model consists of a set of physical equations for avalanche propagation associated with a statistical formalism adapted to the input–output data structure. The friction law includes at least one latent friction coefficient. The Bayesian paradigm and the associated simulation techniques assist considerably in performing the inference and taking estimation errors into account for prediction. Starting from the general case, simplifying hypotheses allows computing the predictive distribution of high return periods on a case-study. Only release and runout altitudes are considered so that the model can use the French database. An inversible propagation model makes it possible to work with the latent friction coefficient as if it is observed. Prior knowledge is borrowed from an avalanche path with similar topographical characteristics. Justifications for the working hypotheses and further developments are discussed. In particular, the whole approach is positioned with respect to both deterministic and stochastic hydrology.  相似文献   

星载海洋高度计海面回波信号的统计特性分析     

吴晓辉  张晓辉 《海洋技术学报》2005,24(3):10-13,21

论文首先从理论上简要阐述了星载海洋高度计海面回波的散射机理和回波信号后向散射模型;其后,利用Matlab数学工具,通过对我国＂神州四号＂飞船下传的大量高度计观测数据进行IQ采样数据提取、数据处理以及统计分析,进行了星载海洋高度计海面回波信号的统计特性分析与研究.  相似文献   

Structural Types of Sea Embankment and Their Stability Analysis   总被引：1，自引：0，他引：1  

MAO Changxi  DUAN Xiangbao  MAO Peiyu Prof. Senior Engineer  Hydraulic Engineering Department  Nanjing Hydraulic Research Institute 《中国海洋工程》1998,(3)

In this paper based on investigation on the structural types of sea embankments in thesoutheast coastal area of China,as well as the related tidal stages,waves and strength of marine soils,thefinite element method(FEM)calculations for seepage flow stability,including the overall stability againstsliding and local stability of sloping surface under the action of tidal stage and waves are carried out.Acomparison of the computational results of FEM for single circular slip,composite circular slip andgeogrid reinforcement against sliding shows that for calculation of stability against sliding of marine softsoil foundation it is even more reasonable to use the composite circular slip.The stability of sloping typesea embankment against sliding is slightly better than that of the vertical face type;for the combination ofthree defences(wave,scour and seepage defences)the sea embankment structural type of a compositecross section with a platform should be a good one,but it still should be suitable to local condit  相似文献