Flow separation and vertical motions in a tidal flow interacting with a shallow-water island     

Laurent White  Eric Wolanski 《Estuarine, Coastal and Shelf Science》2008

This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia), lying perpendicular to tidal flow in shallow waters. At ebb and flood, attached (stable) eddies develop in the wake where swirls of turbidity suggest that sediment-laden waters are brought to the surface as a result of vertical transport. Both eddy and tip upwellings are encountered in the tidal flow around Rattray Island but there is currently no clear-cut answer as to which secondary flow generates upwelling with the largest intensity. This paper addresses this specific issue through idealized and realistic high-resolution numerical experiments. The analysis is supported by physical arguments based on the theory of flow separation. Given Rattray's geometry and surrounding bathymetry, the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity. The results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at Rattray Island.  相似文献   

两步解法用于求解线阵CCD影像外方位元素     

龚辉  姜挺  江刚武  杨靖宇  纪松 《测绘科学》2009,34(2)

在线阵CCD影像外方位元素的求解过程中,外方位元素之间的相关性,导致法方程病态,最小二乘估计值误差较大。本文在分析以往解决方法的基础上,提出采用两步解法求解线阵CCD影像的外方位元素。该算法的实质是选择一个比单位矩阵更合适的正则化矩阵。试验结果表明该算法能有效地克服线阵CCD影像外方位元素间的相关性,定位精度较高,定向点精度在1个像素内,检查点精度在1.5个像素内。  相似文献   

基于形态学的海洋锋形态特征提取          下载免费PDF全文

薛存金  苏奋振  周军其  郭衍游  仉天宇 《海洋科学》2008,32(5):57-61

根据形态学梯度理论:不同尺寸的结构元素适合不同空间尺度的特征提取,结构元素尺寸的过大或者过小都会达不到最佳的特征边缘提取效果,从结构元素的尺寸δ与海洋锋横断面宽度γ和海流流幅的空间尺度λ的理论关系图推导中,提出δ,γ和λ的最佳定量关系:δ=γ/2,且δ<=λ/2,旨在对海洋锋形态特征进行提取。最后,以黑潮和墨西哥湾流为实验数据,进行海洋锋形态特征的自动提取,实验结果表明该定量关系的正确性和有效性。  相似文献   

富钴结壳中成矿元素的微区分布特征及其地质意义   总被引：2，自引：0，他引：2  

赵宏樵  郑存江  初凤友  王笑笑 《海洋学研究》2009,27(2):84-89

采用X射线荧光光谱仪,对CCLLD27站位富钴结壳中8个主要成矿元素(Mn、Fe、Co、Cu、Si、Al、Ca和Ti元素)含量的分布特征进行了微区扫描和人工分层样品方法的分析,结果表明:(1) 成矿元素Mn、Fe、Co和Cu的微区变化很大:Mn与Co元素的微区分布特征相似,而Fe和Cu元素的微区分布特征则相反.主要造岩元素Si和Al的微区分布特征基本类似;Ca元素的微区变化较大,在近底部的基岩层其含量达到最高峰值.Ti元素的微区分布特征与Mn、Co元素微区分布特征接近.(2) 微区扫描与人工分层样品两种不同测试方法所得的结果基本一致,说明微区扫描方法具有一定的可靠性,能反映富钴结壳在不同生长时代各成矿元素含量的变化特征.(3) 富钴结壳微区元素分布特征的研究,有助于对结壳不同成矿阶段各种不同成矿作用的定性评估.  相似文献   

青海省长宁遗址沉积物元素对晚全新世人类活动和气候变化的响应   总被引：3，自引：2，他引：1  

董广辉  贾鑫  安成邦  汪海斌  刘姣  马敏敏 《海洋地质与第四纪地质》2008,28(2):115-119

通过对青海省长宁遗址晚全新世沉积剖面OC、P、Ba、Mn、S、K2O、Pb、As、Al2O3、Fe2O3和Cu的化学成分分析及磁化率分析,研究了该时期沉积物元素含量对人类活动和气候变化的响应。结果表明,齐家文化时期(4300～3900aBP)至汉代(202BC—220AD)之间的气候恶化使沉积物中上述元素含量显著下降,齐家文化时期和汉代的人类活动也对沉积物元素含量产生了影响,不同方式的人类活动对沉积物元素含量的影响存在差异。  相似文献   

Source of and potential bio-indicator for the heavy metal pollution in Ny-(A)lesund, Arctic     

Wang Xiaofei  Yuan Linxi  Luo Honghao  Long Nanye  Wang Yuhong  Sun Liguang 《极地研究(英文版)》2007,18(2)

Three kinds of tundra plant samples including Dicranum angnstum(a type of boreal bryophyte) , PuccineUia phryganodes (a type of fringy p/ant),Salix polaris (a type of vascular plant) and surface soil were samples in 200 at Ny-Alesund of the Arctic.The levels of eight heavy metal elements (Hg, Pb, Cd, Cu, Zn, Ni, Fe and Mn) and three metal-like dements (As, Se, Sr) in the plant and soil samples of the areas within previous coal mining activities are significantly higher than those of other areas.The relative accumulation of these elements in these tundra plant samples is consistent with the one in the soft samples, especially in the areas affected by previous coal-mining activities.Thus, the pollution is apparently from local coal mining activity.Dicranum angustum has the highest concentrations among those elements, and it can be a good bio-indicator for heavy metal pollution in Ny(A)lesund.Though Ny(A)lesund is less polluted by heavy metal than nearby Northern European human living areas, but much more than the tundras of the Alaska, Greenland and the Antarctic.  相似文献   

Transverse and longitudinal fluid flow modelling in fractured porous media with non‐matching meshes     

Behnam V. Damirchi  Marcelo R. Carvalho  Luís A. G. Bitencourt  Osvaldo L. Manzoli  Daniel Dias‐da‐Costa 《国际地质力学数值与分析法杂志》2021,45(1):83-107

A new discrete fracture model is introduced to simulate the steady‐state fluid flow in discontinuous porous media. The formulation uses a multi‐layered approach to capture the effect of both longitudinal and transverse permeability of the discontinuities in the pressure distribution. The formulation allows the independent discretisation of mesh and discontinuities, which do not need to conform. Given that the formulation is developed at the element level, no additional degrees of freedom or special integration procedures are required for coupling the non‐conforming meshes. The proposed model is shown to be reliable regardless of the permeability of the discontinuity being higher or lower than the surrounding domain. Four numerical examples of increasing complexity are solved to demonstrate the efficiency and accuracy of the new technique when compared with results available in the literature. Results show that the proposed method can simulate the fluid pressure distribution in fractured porous media. Furthermore, a sensitivity analysis demonstrated the stability regarding the condition number for wide range values of the coupling parameter.  相似文献   

On the causes of pressure oscillations in low‐permeable and low‐compressible porous media     

Joachim Berdal Haga  Harald Osnes  Hans Petter Langtangen 《国际地质力学数值与分析法杂志》2012,36(12):1507-1522

Nonphysical pressure oscillations are observed in finite element calculations of Biot's poroelastic equations in low‐permeable media. These pressure oscillations may be understood as a failure of compatibility between the finite element spaces, rather than elastic locking. We present evidence to support this view by comparing and contrasting the pressure oscillations in low‐permeable porous media with those in low‐compressible porous media. As a consequence, it is possible to use established families of stable mixed elements as candidates for choosing finite element spaces for Biot's equations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

基于pXRF的荞麦山铜多金属矿床元素富集规律研究     

张明明  龙瑾潇  周国玉  焦峻嵚  方红东 《矿床地质》2022,41(3):643-658

大数据技术在地学领域的应用越来越广泛,大数据思维为地学研究开辟了新的思路。从数据出发,以数据驱动模式去分析地质问题,在元素分布特征分析、矿床地化异常识别等方面较传统地学分析方法有着明显的优势。文章基于便携式X荧光分析仪（pXRF）测试的原位、无损、快捷、多元素分析等优点,对宣城矿集区内的荞麦山铜多金属矿床岩芯进行高密度的全数据原位采集,使用主成分分析（PCA）、多元逐步线性回归等方法进行量化分析。2种方法均表明,荞麦山铜多金属矿床中元素Mg、Ca、Mn、Co、As、Se、Ag、Hg、U和成矿元素Cu、Fe、S、W存在正相关关系;钻孔矿化和蚀变特征、铜硫矿石、钨矿石、石英砂岩均表现出不同的元素组合,特别是主成分综合得分（PCA）和第一主成分（PC1）元素对钻孔成矿区具有较好的指示效果;逐步多元线性回归分析进一步量化了元素富集规律,对成矿元素的拟合能够较好地与钻孔信息形成对应。因此,pXRF高密度的原位测量能够快速获取全面、准确的元素数据,分析结果能够直观反映荞麦山铜多金属矿床各元素的深度空间分布情况及量化相关关系,对深部地球化学特征的恢复和找矿提供帮助。  相似文献   

安徽青阳—九华山复式岩体的成因及成矿潜力——来自锆石Hf同位素和微量元素的证据     

叶龙翔  张达玉  汪方跃  陈雪锋  张飞  席晓晨  周涛发 《地质论评》2022,68(4):1278-1300

青阳—九华山复式岩体是安徽南部地区出露面积最大、最具代表性的复式岩体,该复式岩体的岩浆源区、演化过程和成矿联系等问题仍需要进一步查明。在前期对青阳—九华山复式岩体的地质、地球化学特征研究基础上,本文进一步开展了锆石微量元素与Hf同位素分析与研究。结果显示,青阳—九华山复式岩体4个阶段从早到晚（花岗闪长岩二长花岗岩正长花岗岩细粒花岗斑岩）,晚期(第三、第四阶段)比早期(第一、第二阶段)岩浆岩的锆石εHf（t）值呈显著增高趋势,岩浆形成温度升高（705.3℃ 715.9℃ 827.1℃ 805.5℃）,氧逸度降低（93.8 149.170.1 69.9）。进一步分析认为,青阳—九华山复式岩体源于同一具有壳幔混源的岩浆源区,随着时间的演化,岩浆房中幔源组分比例逐渐增高,幔源物质的加入,不仅提高了晚期岩浆形成温度,一定程度改变了源区组成。青阳—九华山复式岩体4个阶段花岗岩均经历了榍石、角闪石、金红石、斜长石等矿物的分离结晶,晚期（第三、第四阶段）花岗岩相比早期（第一、第二阶段）花岗岩具有更高的分异程度。青阳—九华山复式岩体中第一、第二阶段花岗岩具有较好的W—多金属矿床成矿潜力。  相似文献