华南前汛期降水变率的分析   总被引：23，自引：2，他引：21       下载免费PDF全文

郭其蕴  沙万英 《应用气象学报》1998,(Z1)

利用华南１６个站１９５１～１９９６年逐年、月和候降水量资料,分析了前汛期（４～６月）总降水量及前汛期开始期的变化特征．结果表明,全区前汛期总降水量变化有相当好的一致性．以降水异常的空间分布基本可划分成６种类型．根据候降水量变化,逐年前汛期开始期大体可分成４类,即：全区偏早（１４年）;全区偏晚（１６年）;东部早西部晚（７年）和东部晚西部早（９年）．总之,无论是前汛期降水量还是前汛期开始日期都具有明显的年际变化和年代际变化特征  相似文献   

一个以遗传算法为基础的结构可靠性分析方法   总被引：5，自引：0，他引：5  

赵衍刚  江近仁 《地震工程与工程振动》1995,15(3):47-58

本文首先总结了一次二阶矩法在结构可靠性分析时的五个弱点。针对其在寻求验算点时需要求极限状态函数的导数以及在处理多峰性极限状态函数时存在的不收敛或收敛于局部验算点等弱点，探讨了将遗传算法应用于结构可靠性分析的可能性，并在分析其应用时存在的具体问题的基础上提出了一个以智能生物为基础的遗传算法。本文的分析计算表明：遗传算法在结构可靠性分析中是适用的，它可以克服一次二阶矩法在求解验算点时存在的几个弱点。本  相似文献   

高含沙河流的低温输沙效应——以黄河上游巴彦高勒站为例          下载免费PDF全文

白涛  慕鹏飞  张明 《水科学进展》1990,31(2):194-202

黄河是世界上含沙量最高的河流,其上游沙漠宽谷河段的冲沙输沙效应受来水来沙和地形条件变化等影响。为研究高含沙河流在低温条件下的输沙效应,通过引入水温因子,建立了黄河上游沙漠宽谷河段巴彦高勒站的输沙率模型。基于First Optimization平台的通用全局优化算法率定参数,验证了输沙率模型,量化了高含沙河流的低温输沙效应。结果表明:① 水温越低(1~7 ℃),河道输沙率越大,表明水温对河道输沙率的影响主要表现在低水温时期;② 任意一种工况下,水温1 ℃时河道输沙率约为25 ℃时的2.5倍;③ 低水温(5 ℃)较常温(16.6 ℃)下的河道输沙率提高了40.7%,在黄河上游开河低温期进行大流量冲沙输沙是水沙调控的最佳时机。研究成果以期为黄河上游沙漠宽谷河段低水温高效冲沙输沙和其他寒区高含沙河流的治理提供技术支撑。  相似文献   

Some results comparing Monte Carlo simulation and first order Taylor series approximation for steady groundwater flow     

L. Jones 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):179-190

The expected head and standard deviation of the head from the first order Taylor series approximation is compared to Monte Carlo simulation, for steady flow in a confined aquifer with transmissivity as a random variable. Emphasis is on the effect of changes in the covariance structure of the transmissivity, and pumping rates, on the errors in the first order Taylor series approximation. The accuracy of the first order Taylor series approximation is found to be particularly sensitive to pumping rates. With significant pumping the approximation is found to under estimate both the expected drawdown and head variance, and the error increases as the pumping rate increases. This can lead to large errors in probability constraints based on moments from the first order Taylor series approximation.  相似文献   

Case history of a slip-type rockburst     

T. J. Williams  C. J. Wideman  D. F. Scott 《Pure and Applied Geophysics》1992,139(3-4):627-637

First-motion analyses of digital seismic records and an assessment of damage provided conclusive evidence that a fault-slip source mechanism was responsible for a Richter magnitude 2 that occurred at the Lucky Friday Mine on April 13, 1990. This event was the first time that movement along an argillite bed had been observed after the macroseismic monitoring system had been installed. The physical evidence of a shear-slip type failure established confidence in using double-couple, first-motion analyses for the macroseismic system. The U.S. Bureau of Mines is conducting this research as part of its mission to enhance safety by reducing rockburst hazards in mines.  相似文献   

地面地震初至波层析反演复杂表层速度结构方法   总被引：1，自引：0，他引：1  

罗省贤  李录明 《地球科学进展》2004,(Z1)

针对复杂表层结构的反演问题,作者研究了一套利用地面地震初至波层析反演表层速度结构的理论、方法和软件系统。该方法利用了地面地震直达波、迥折波、折射波以及三者组合的初至波,并采用具有空间变速优势的层析反演,可获得任意介质类型的表层速度结构。该方法的优点是野外施工简单(不需要在井中激发、接收),反演精度高,适应性强,反演所得到的表层速度结构可直接用于环境与工程项目的表层地质结构调查和评价。  相似文献   

第一勘探类型铀矿床的主要指标及合理勘探网度的探讨     

曾庆录  刘世明 《铀矿地质》1994,10(1):20-24

本文通过苏崩矿床不同勘探网度的主矿体厚度、品位及其变化系数和储量等主要参数对比研究，提出第一勘探类型铀矿床应具的规模、稳定性、连续性指标及各级储量的勘探工程间距。  相似文献   

Erosion of trust in government consultation will impede the creation of environmental policy     

《Marine Policy》2017

Conflicts over resource are becoming increasingly frequent as human development accelerates and resource limitations become evident. The impact of these conflicts is felt disproportionately by Indigenous Peoples, who despite international recognition that they must be consulted over resource extraction, have not been adequately included in policy development. As creation of effective environmental policy relies on meaningful consultation of all stakeholders, there is now a global outcry surrounding this eroded process. In British Columbia, Canada, a lack of meaningful government consultation has resulted in the approval of large-scale developments (the Site C Hydroelectric Dam and the Pacific Northwest Liquefied Natural Gas terminal) that are directly opposed by multiple stakeholders (First Nations, the academic community, conservation organizations, and other concerned citizens). A key component of the consultation process, trust, is explored here. Specifically, how poor government consultation erodes stakeholder trust in the consultation process. This trust is essential if holistic environmental policy, policy that protects both the environment and the economy, is to be created.  相似文献   

华南水汽涡旋输送分析     

高绍凤 《热带气象学报》1999,15(3):240-246

水汽输送按时空分离为平均输送和涡旋输送。对华南区域１９９４年前汛期的水汽输送所做的分析表明,季平均各种涡旋输送量与总输送量相比不到１０％,月平均气柱涡旋输送量约占总输送量的１０％—２０％。在夏季风爆发前和暴雨期,旬平均水汽涡旋输送强烈,最大可达到总输送量的５至６倍,这时期不能用平均输送代表总输送。最后给出了用气候平均量计算的各时段水汽输送对总输送的代表性的估计。  相似文献   

Wavefield interpolation in 3D large‐step Fourier wavefield extrapolation          下载免费PDF全文

Gaoxiang Chen  Li‐Yun Fu  Wei Wei  Weijia Sun 《Geophysical Prospecting》2018,66(2):311-326

Extrapolating wavefields and imaging at each depth during three‐dimensional recursive wave‐equation migration is a time‐consuming endeavor. For efficiency, most commercial techniques extrapolate wavefields through thick slabs followed by wavefield interpolation within each thick slab. In this article, we develop this strategy by associating more efficient interpolators with a Fourier‐transform‐related wavefield extrapolation method. First, we formulate a three‐dimensional first‐order separation‐of‐variables screen propagator for large‐step wavefield extrapolation, which allows for wide‐angle propagations in highly contrasting media. This propagator significantly improves the performance of the split‐step Fourier method in dealing with significant lateral heterogeneities at the cost of only one more fast Fourier transform in each thick slab. We then extend the two‐dimensional Kirchhoff and Born–Kirchhoff local wavefield interpolators to three‐dimensional cases for each slab. The three‐dimensional Kirchhoff interpolator is based on the traditional Kirchhoff formula and applies to moderate lateral velocity variations, whereas the three‐dimensional Born–Kirchhoff interpolator is derived from the Lippmann–Schwinger integral equation under the Born approximation and is adapted to highly laterally varying media. Numerical examples on the three‐dimensional salt model of the Society of Exploration Geophysicists/European Association of Geoscientists demonstrate that three‐dimensional first‐order separation‐of‐variables screen propagator Born–Kirchhoff depth migration using thick‐slab wavefield extrapolation plus thin‐slab interpolation tolerates a considerable depth‐step size of up to 72 ms, eventually resulting in an efficiency improvement of nearly 80% without obvious loss of imaging accuracy. Although the proposed three‐dimensional interpolators are presented with one‐way Fourier extrapolation methods, they can be extended for applications to general migration methods.  相似文献