Velocity and Sediment Concentration Profiles in Sediment-Laden Flows     

杨树清  Soon-KeatTAN  Siow-YongLIM 《中国海洋工程》2004,18(2):229-244

A theoretical analysis of velocity profiles in sediment-laden flows is presented by means of Prandtl-Karman mixing length theorem. The study shows that the upward velocity of liquid-phase caused by settling sediment leads to the invalidity of the log-law and Rouse equation. The theoretical analysis takes into account the upward velocity and shows: 1) the mean velocity in sediment-laden flows follows the log-law, but the Karman constant reduces in the main flow region, 2) sediment concentration reduces the mixing length of fluid particles, 3) flow resistance reduces with the presence of sediment concentration, and 4) the sediment concentration profile deviates from the well know Rouse equation. The experimental data agree well with the equations derived on the basis of non-zero wall velocity. It is found that the wall-normal velocity should not be neglected for density gradient flows because it induces more than for pure water flows.  相似文献   

Silting in the Lower Courses of Tidal Sluices in China   总被引：2，自引：0，他引：2  

张金善  黄建维杨红 《中国海洋工程》2004,18(1):137-148

Serious sediment deposition often occurs after the construction of tidal sluices in snrall or medium-sized tidal muddy estuaries, so desilting or dredging is needed to meet the demands of flood diseharge, saltwater retaining, and navigation in those areas. In this paper, the problem of sediment deposition induced by construction of tidal sluices is analyzed.Different problems of silting near tidal sluices for different types of estuaries are summed up. at the same time, corresponding methods are given to solve these probleras, and a few successful examples are also given. The idea of comprehensive regulation and utilization of estuaries is put forward, and some proposals for solution of sediment deposition in this kind of estuaries are made.  相似文献   

Chloride transfer in cement‐based materials. Part 1. Theoretical basis and modelling     

K. Bourbatache  O. Millet  A. Aït‐Mokhtar  O. Amiri 《国际地质力学数值与分析法杂志》2013,37(11):1614-1627

In this first part of the work, we develop macroscopic models for migration and diffusion–migration of ionic species in saturated porous media, based on periodic homogenization. The prior application is chloride transport in cementitious materials. The dimensional analysis of Nernst–Planck equation lets appear to dimensionless numbers characterizing the ionic transfer in the porous medium. Using experimental data obtained from electrodiffusion tests on cement‐based materials (Part II), these dimensionless numbers are linked to the perturbation parameter ?. For a strong imposed electrical field, the asymptotic expansion of Nernst–Planck equation leads to a macroscopic model where the migration is predominant. For a weak imposed electrical field or in natural diffusion, we obtain a macroscopic model coupling diffusion and migration at the same order. In both models, the expression of the homogenized diffusion tensor is identical and only involves the geometric properties of the material microstructure. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

An enhanced homogenization approach for masonry structures with compressible joints. Application to hearth thermomechanical computations     

N. J. Mathieu  K. Sab  S. A. Zaïmi 《国际地质力学数值与分析法杂志》2012,36(9):1102-1124

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Vertical Distribution of Momentum Exchange Coefficient and Sediment Concentration in Estuarine and Coastal Waters     

黄惠明  王义刚  闻云呈  祝慧敏 《中国海洋工程》2010,(4)

Vertical structures of momentum exchange coefficient and sediment concentration are the keys in the research on estuarine and coastal suspended sediment transport. Based on the parabolic mixing length distribution pattern,the distribution pattern of vertical momentum exchange coefficient which is suitable for estuarine and coastal waters is constructed. A comparison with steady flow and measured momentum exchange coefficient during one tidal cycle in the Menai Strait of England shows that the result of this...  相似文献   

Les camptonites du mont Cameroun,Cameroun, Afrique     

Ismaïla Ngounouno  Bernard Déruelle  Raymond Montigny  Daniel Demaiffe 《Comptes Rendus Geoscience》2006,338(8):537-544

Camptonites have been discovered at Mount Cameroon. They contain phenocrysts of olivine + clinopyroxene + plagioclase ± kaersutite ± bi and ocelli of nepheline or analcite and carbonates. ⁸⁷Sr/⁸⁶Sr_i values are similar to those of the basalts of Mount Cameroon $(\approx 0.7033)$. The camptonites are interpreted as resulting from fractional crystallization of a basaltic magma generated by a low degree of melting of an infra-lithospheric metasomatized mantle tapped by huge lithospheric cracks. To cite this article: I. Ngounouno et al., C. R. Geoscience 338 (2006).  相似文献   

华南南流江流域ESRE复合系统协调发展研究     

阚兴龙  周永章  李辉 《热带地理》2012,32(6):658-663

以流域ESRE(经济-社会-资源-环境)复合系统理论为指导,构建华南南流江流域各子系统协调发展度测评指标体系,优化传统区域经济环境协调发展测度模型,对南流江流域上游玉林、中游博白、下游北海3个地区的经济社会与资源环境发展协调度进行测算.结果显示:近年来南流江流域整体经济社会和资源环境的协调水平基本稳定,上游、中游处于良好协调状态,下游地区达到优质协调状态.随着流域工业化进程的加快,流域面临的生态环境压力也在增大.  相似文献   

重庆市统筹城乡发展管理举措及实施评价——以江北区为例     

宗会明  谷艳博  桂林 《热带地理》2012,32(6):652-657

统筹城乡发展已经上升为国家战略,学术界对其研究方兴未艾,但统筹城乡发展与规划的系统性和复杂性使规划管理与实践工作面临诸多问题.研究以重庆市江北区为案例分析了近几年来重庆市统筹城乡发展在产业规划、社会政策及城乡规划调整方面的管理政策和举措,并对这些举措的实施对农村地区的战略定位、经济发展、基础设施建设、社会保障、公共服务供给等方面带来的影响进行了合理评价.研究发现重庆市统筹城乡改革的各项规划政策内容丰富,在城乡经济,尤其是农村地区的经济、社会、规划体系等方面都收到了较好的成效.但其管理和操作过程属于一种“政府主导”的发展模式,市场力量和公众参与并未得到充分重视,在一定程度制约了重庆统筹城乡模式推广的普遍性和发展的可持续性.  相似文献   

Adaptation of the optimal fingerprint method for climate change detection using a well-conditioned covariance matrix estimate   总被引：3，自引：3，他引：0  

Aurélien Ribes  Jean-Marc Azaïs  Serge Planton 《Climate Dynamics》2009,33(5):707-722

The “optimal fingerprint” method, usually used for detection and attribution studies, requires to know, or, in practice, to estimate the covariance matrix of the internal climate variability. In this work, a new adaptation of the “optimal fingerprints” method is presented. The main goal is to allow the use of a covariance matrix estimate based on an observation dataset in which the number of years used for covariance estimation is close to the number of observed time series. Our adaptation is based on the use of a regularized estimate of the covariance matrix, that is well-conditioned, and asymptotically more precise, in the sense of the mean square error. This method is shown to be more powerful than the basic “guess pattern fingerprint”, and than the classical use of a pseudo-inverted truncation of the empirical covariance matrix. The construction of the detection test is achieved by using a bootstrap technique particularly well-suited to estimate the internal climate variability in real world observations. In order to validate the efficiency of the detection algorithm with climate data, the methodology presented here is first applied with pseudo-observations derived from transient regional climate change scenarios covering the 1960–2099 period. It is then used to perform a formal detection study of climate change over France, analyzing homogenized observed temperature series from 1900 to 2006. In this case, the estimation of the covariance matrix is only based on a part of the observation dataset. This new approach allows the confirmation and extension of previous results regarding the detection of an anthropogenic climate change signal over the country.  相似文献   

Along-strike variations of P–T conditions in accretionary wedges and syn-orogenic extension,the HP–LT Phyllite–Quartzite Nappe in Crete and the Peloponnese     

Laurent Jolivet  Fabien Trotet  Patrick Monié  Olivier Vidal  Bruno Goffé  Loïc Labrousse  Philippe Agard  Bad'r Ghorbal 《Tectonophysics》2010,480(1-4):133-148

Syn-orogenic detachments in accretionary wedges make the exhumation of high-pressure and low-temperature metamorphic rocks possible with little erosion. The velocity of exhumation within the subduction channel or the accretionary complex, and thus the shape of P–T paths, depend upon the kinematic boundary conditions. A component of slab retreat tends to open the channel and facilitates the exhumation. We document the effect of slab retreat on the shape of P–T paths using the example of the Phyllite–Quartzite Nappe that has been exhumed below the Cretan syn-orogenic detachment during the Miocene in Crete and the Peloponnese. Data show a clear tendency toward colder conditions at peak pressure and during exhumation where the intensity of slab retreat is larger. This spatial evolution of P–T gradient is accompanied with an evolution from a partly coaxial regime below the Peloponnese section of the detachment toward a clearly non-coaxial regime in Crete.  相似文献