数值模拟气流特征和砾石几何参数对床面空气动力学粗糙度的影响     

王晓  张伟民 《中国沙漠》2014,34(4):943-948

本文应用流体计算软件FLUENT6.3,采用非结构化网格划分技术模拟了气流特征和砾石几何参数对床面空气动力学粗糙度的影响。结果表明：空气动力学粗糙度（z₀）与风速（u）、摩阻速度（u_*）之间存在定量关系：z₀=a exp（bu/u_*）。砾石高度对空气动力学粗糙度的影响显著优于砾石直径,空气动力学粗糙度随砾石密度的变化比较复杂,先增加后减小。FLUENT在模拟风洞砾石床面动力学过程中的成功应用,是我们在研究方法上的一次有益尝试。  相似文献   

Extending Service Life of Household Water Filters by Mixing Metallic Iron with Sand     

Chicgoua Noubactep  Sabine Caré  Fulbert Togue‐Kamga  Angelika Schöner  Paul Woafo 《洁净——土壤、空气、水》2010,38(10):951-959

The use of metallic iron filters (Fe⁰ filters) has been discussed as a promising low‐cost option for safe drinking water production at household level. Filter clogging due to the volumetric expansive nature of iron corrosion has been identified as the major problem of Fe⁰ filters. Mixing Fe⁰ and sand (yielding Fe⁰/sand filters) has been proposed as a tool to extent filter service life. However, no systematic discussion rationalizing Fe⁰/sand mixtures is yet available. This communication theoretically discussed suitable Fe⁰/sand proportions for efficient filters. Results suggested that Fe⁰/sand filters should not contain more that 50 vol% Fe⁰ (25 wt% when Fe⁰ is mixed with quartz). The actual Fe⁰ percentage in a filter will depend on its intrinsic reactivity.  相似文献   

重庆地区地震统计单元b值和ν_4值的讨论     

秦娟  李光  王宏超 《四川地震》2010,(1)

b值和ν4是地震安全性评价工作中进行地震危险性概率计算的两个重要参数,其取值是否合理将影响地震危险性计算结果的合理性.本文采取两种不同的计算方法对重庆地区的b值和ν4进行计算,并对于这两个参数进行了讨论.我们认为取 b=1.19和ν4=2.48基本上是合理的,该结果对重庆地区开展地震安全性评价工作和地震中长期预报工作具有一定的参考价值.  相似文献   

海岸地区致灾台风暴潮的长期分布模式   总被引：2，自引：0，他引：2       下载免费PDF全文

董胜  郝小丽  李锋  刘德辅 《水科学进展》2005,16(1):42-46

考虑台风导致的高水位和海浪波高对风暴潮灾害的贡献,对1949年以来影响青岛地区的台风暴潮进行了抽样统计.基于二维的泊松冈贝尔逻辑分布模式,对海岸地区的致灾风暴潮进行了长期的随机分析.与传统的警戒水位法不同,新模式能够反映多种环境荷载的综合作用,推算了青岛地区的特大台风暴潮灾害的重现期.计算结果显示,二维复合分布模式适合于描述台风暴潮过程中极值水位与相应波高的联合概率,所得结论对青岛地区的防潮减灾规划和工程建设具有指导意义.  相似文献   

1972～2001年四川及邻区大震危险性预测研究的检验与思考     

黄圣睦  董瑞英 《四川地震》2004,(2):1-7

回顾了1972～2001年间省内外地震学者对四川震情研究的44篇文献中所提出的预测意见和实际检验情况,对其中的主要预测依据、预报能力、应用条件分别作了进一步分析。最后归纳了近期、中期、中短期3类强震趋势活动图像特征：近期危险性分析侧重地震带是否可能进入大震活跃幕;中期危险性分析侧重大震活跃幕的类型及窗口、相关、信号等地震是否发生;中短期危险性分析侧重中强震的条带、丛、环异常及诱发地震、逼近地震、缺震事件。实践表明,图像分析中尤应注意与孕震环境由大至小的整体分析和发展阶段的个性研究相结合。  相似文献   

Trends in atmospheric Cd deposition recorded in a 64-meter long ice-core and a 5-m snow pit record from Devon Island, Nunavut, Canada     

Yaping WANG Chunxue XU Suming WANG Ziyi AN 《中国地球化学学报》2006,25(B08):15-15

Along with the rapid development of science and technology, natural matter and energy are further exploited and used. The pollution imposed on nature has also sharply increased. Only do we know the pollution history, can we make a correct appraisal of local environment, get the hold of the main cause of environmental pollution, and then take the effective measures to control the environment？ The evolution of heavy metal concentrations with time in the soil environment in the southern suburbs of Beijing were studied by using annual growth rings of trees. The absorption of 12 elements by different tree species in the same soil type was studied according to their absorption coefficients. The study indicated the differences in adsorption of elements by different species of trees. The adsorption coefficients of the elements Zn, Cd and P are higher. The correlations of nine elements （Na, K, Cu, Zn, As, Sr, Cd, Ba and Pb） in growth rings of poplar trees and those in soils near their roots show that the element contents in growth rings have a positive correlation with the contents in soils near the roots. Based on the logarithmic linear correlation model, the evolution of the contents of the elements Cu, Zn, As, Cd, Ba and Pb in soils from 1982 to 2004 was deduced. The trees have the characters of confirming year precisely, long life and widespread distribution. They are the ideal objects of study on environmental pollution changes. At present, research in China in this aspect is less, and the field of research is expected to further expand. This method can be used to provide richer and more scientific information on the history of environmental pollution and changes during modem urbanization in the past few decades and predicting the evolutionary trend of pollution change.  相似文献   

粗糙床面风廓线统一对数区的空气动力学粗糙度及其空间变异特征   总被引：1，自引：1，他引：0  

梅凡民  张宁宁  席媛  刘秀秀 《中国沙漠》2018,38(3):445-454

为了进一步理解粗糙床面阻力效应,减小空气动力学粗糙度测试中的不确定性,依据风沙风洞测试的3类粗糙元（细高粗糙元、孔隙粗糙元和粗矮粗糙元）覆盖的39个粗糙床面在不同自由风速下的风廓线数据,提出了风廓线统一对数区的概念并得出以下结论：粗糙床面风廓线统一对数区范围约在0.1～0.3 h至边界层顶部,空气动力学粗糙度是变应力层内床面对气流阻力效应的垂向平均;在统一对数区内拟合的空气动力学粗糙度的垂向变异分为先增后减型（概率为71%）、减小型（20%）和增加型（9%）等类型,而采用统一对数区的空气动力学粗糙度可以避免垂向变异带来的不确定性;统一对数区的无量纲空气动力学粗糙度随粗糙元密度以幂函数形式增加的特征,进一步表明该指标能更好地表征粗糙床面对气流阻力效应;尾涡流风廓线统一对数区的空气动力学粗糙度约为街流区1~5倍,表明街流区风廓线统一对数区的空气动力学粗糙度是模拟跃移起动更合适的参数。  相似文献   

半干旱区榆中地表粗糙度年变化及影响机理   总被引：1，自引：0，他引：1       下载免费PDF全文

姚彤  张强  尹晗 《应用气象学报》2014,25(4):454-462

利用2006年6月—2010年12月兰州大学半干旱气候与环境观测站 (SACOL) 观测资料,分析了黄土高原自然植被下垫面榆中地表粗糙度时间变化特征,考虑到地形、植被物理特征以及降水和热力条件的影响,分析了东南风向和西北风向粗糙度年变化规律及其影响机理,并分别给出这两个风向归一化粗糙度与时间的拟合关系式。研究发现:对于非均一下垫面,由于地形起伏和下垫面植被差别造成的不同风向粗糙度差异显著。选取东南风向和西北风向,这两个风向的地表粗糙度无论是量级还是年变化特征都有很大差别,且由于地形和植被的差别,东南风向粗糙度年变化趋势与稳定度年变化趋势一致,粗糙度与稳定度存在一定相关关系,而西北风向粗糙度年变化趋势与降水量年变化趋势一致,粗糙度与降水量相关性较好。  相似文献   

非均匀风影响下风力机三维气动粘性流场的数值模拟     

周胡  赵文超  万德成 《海洋工程》2015,33(1):90-99

基于面向对象的开源软件OpenFOAM,选择美国国家新能源实验室(NREL)Phase VI风力机为对象,对以往研究较少的非均匀来流风速作用下风力机三维气动粘性流场进行数值模拟。采用较为接近于真实情况的指数型风剖面,计算了轮毂处风速分别为5、10、15和25 m/s四种工况下的叶片表面压力分布、叶片的推力、尾涡等气动力数据,并与均匀来流风速下的风力机气动力学性能进行详细的对比,探讨非均匀风剖面对风力机流场结构和流动特性影响的物理现象和规律。  相似文献   

Long‐term demographic and reproductive trends in Ciona intestinalis sp. A          下载免费PDF全文

Luigi Caputi  Fabio Crocetta  Francesco Toscano  Paolo Sordino  Paola Cirino 《Marine Ecology》2015,36(1):118-128

Ciona intestinalis sp. A (Tunicata, Ascidiacea) is a marine invertebrate with a widespread distribution and high invasive potential, yet little is known about its ecology. Here, the macrodynamics of demographic and reproductive trends were first determined using archive data covering 2002–2012. Species abundance in the central Tyrrhenian Sea (Campania, Italy ‐ NW Mediterranean) displayed Poisson distribution across 2002–2008, massive die‐off in 2009/2010 and population recovery in 2011/2012. We defined the seasonal ranges of sea surface temperature in which sampling size, animal size and reproductive status reached their highest values. In 2003/2004, self and non‐self fertilization appeared to follow reverse trends across the year. The long‐term recording run here on Ciona intestinalis sp. A provides novel insights into its population biology and ecology, and represents a valuable tool for sampling management and research planning.  相似文献