Sediment dispersal and deposition due to sand mining in the coastal waters of Korea     

Chang S. Kim  Hak-Soo Lim 《Continental Shelf Research》2009

Understanding the impact of marine sand mining operations in a complex coastal environment requires a combined observational and modeling approach. Here, we use field measurements collected during mining operations in Kyunggi Bay, Korea to develop sediment parameters and source conditions for a three-dimensional (3D) sediment transport model built on the Regional Ocean Modeling System (ROMS). The model is run with realistic forcing obtained from a 9 km meteorological model, tides, and river discharges. The resulting vertical and horizontal distributions of sediment show encouraging agreement with the field data, demonstrating markedly different dispersal patterns due largely to the differential settling of the various sand classes. The resulting depositional patterns suggest that only the coarser size classes (500 and 250 μm) particles remain close to the mined site, while finer size classes are widely dispersed. These results suggest that this new methodology of multi-size class, 3D sediment transport modeling is quite promising, and further work is ongoing to include more realistic representation of sediment resuspension processes.  相似文献   

基于支持向量机的砂土液化预测分析   总被引：1，自引：0，他引：1       下载免费PDF全文

师旭超  郭志涛  韩阳 《地震工程学报》2009,31(4):363-366

将支持向量机方法应用于砂土地震液化预测问题.考虑影响砂土液化的因素,选用震级、标贯击数、相对密实度、土层埋深、地震历时、地面运动峰值加速度和震中距7个影响因子作为液化判别指标,建立了砂土液化预测的支持向量机模型.以砂土液化实测数据作为学习样本进行训练,建立相应函数对待判样本进行分类.研究结果表明:支持向量机模型分类性能良好,是砂土地震液化预测的一种有效方法,可以在实际工程中进行推广.  相似文献   

Long-term evolution of sand waves in the Marsdiep inlet. I: High-resolution observations     

Maarten C. Buijsman  Herman Ridderinkhof 《Continental Shelf Research》2008

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Size sorting of fine-grained sediments during erosion: Results from the western Gulf of Lions     

B.A. Law  P.S. Hill  T.G. Milligan  K.J. Curran  P.L. Wiberg  R.A. Wheatcroft 《Continental Shelf Research》2008

Sediment cores from the western Gulf of Lions France were subject to known bottom shear stresses with the goal of understanding size-specific sediment erodibility. On cruises in October 2004, February and April 2005, cores with an undisturbed sediment–water interface were collected along a transect extending seaward from the Tet river mouth. The cores were exposed to increasing shear stresses (0.01–0.4 Pa) onboard the vessel shortly after collection by using a Gust erosion chamber. Samples of the suspensate were collected during the erosion experiments and analyzed for disaggregated inorganic grain size (DIGS) using a Coulter Multisizer IIe. Size-specific mobility plots were generated by dividing the proportion of each grain size in suspension at each shear stress by its proportion in the sediment before erosion. If all grain sizes that make up the bottom sediment are eroded equally from the bed, then mobility equals one for all grain sizes. Values >1 indicate that the suspended sediment is enriched in the size class and values <1 indicate that the size class is enriched in the bed. Results show that in non-cohesive, sandy silts, fine grains (clays and fine silts) are eroded preferentially from the bed at low shear stresses. With increasing bottom stress progressively larger grains are eroded from the bed. In cohesive silts, preferential erosion of the finer sizes no longer occurs, with all sizes up to medium silts eroding at approximately the same rate. Effectively, a sandy silt can be winnowed of its fine grain fraction during erosion while cohesive silts cannot. This difference in the sortability of cohesive and non-cohesive sediment during erosion may control the position and maintenance of the sand–mud transition and the sequestration of surface-adsorbed contaminants.  相似文献   

基于距离和局部Delaunay三角化控制的颗粒离散元模型填充方法研究     

王秀菊  石崇  李德杰  梁邦炎  严晨宇 《岩土力学》2015,36(7):2081-2087

根据颗粒离散元Kelvin 接触力计算模型,分析了圆形颗粒体模拟材料力学特性应具备的条件,在此基础上提出了一种新颗粒模型构建方法。该方法首先在复杂模型域内随机生成种子,然后利用相切条件逐步扩展填充整个区域。填充过程中借助局部Delaunay三角化网格控制新颗粒的生成,采用复杂几何体距离控制颗粒与模型边界的相对位置,对靠近模型边界的颗粒进行容忍性优化填充,从而增加模型颗粒与边界的耦合性。同时对模型孔隙进行再填充,保证每个填充颗粒至少与3个颗粒相切,提高了模型内颗粒间的耦合性和模型的密度。最后采用任意多边形控制材料边界,将模型材料的设置简化为判断点是否在多边形内,简化了复杂模型材料属性的设置过程。结果表明：与膨胀颗粒生成法相比,该方法生成模型重叠量小、颗粒间及颗粒-边界相互耦合、填充率高。因此,颗粒黏结力破坏后不会造成飞溢现象,可适用于任意连通域模型的生成,能更好地实现复杂岩土细观介质变形破坏机制的模拟与研究。  相似文献   

基于岩石颗粒排列方式的低渗透储层应力敏感性分析     

雷刚  董平川  杨书  王彬  吴子森  莫邵元 《岩土力学》2014,35(Z1):209-214

以颗粒堆积模型为基础,考虑了低渗透岩心颗粒不同排列方式和不同变形方式,建立了毛管束模型,并通过颗粒Hertz接触变形原理对毛管变形量进行计算,研究毛管和多孔介质应力敏感性定量表征关系,通过有效毛管分数和毛管变形规律探讨了低渗透储层应力敏感性的作用机制。研究表明,低渗透储层的应力敏感性主要表现为渗透率的应力敏感性,相比于渗透率应力敏感性,孔隙度应力敏感性较弱;低渗透储层应力敏感性与岩石颗粒排列方式、颗粒变形方式、岩石微观孔隙结构、固液界面作用力和启动压力梯度效应等密切相关;考虑有效毛管分数和毛管变形量的多孔介质应力敏感性量化模型可从应力敏感性微观作用机制角度解释低渗透储层应力敏感性。  相似文献   

吹填软土蠕变过程中颗粒与孔隙演化特征分析     

杨爱武  孔令伟  张先伟 《岩土力学》2014,35(6):1634-1640

软土一般具有蠕变特性,蠕变在微观上表现为土颗粒与孔隙的变化。为了解长期变形内在机制,对天津滨海吹填软土原状土与重塑土进行了固结不排水三轴蠕变试验。在围压为75 kPa、偏应力为10 kPa情况下开展多组平行试验,选取蠕变过程中多个时间点的试样进行微观结构测试,提取了颗粒与孔隙变化参数,研究蠕变过程中微结构变化规律。研究结果表明：在文中所受荷载条件长期作用下,颗粒与孔隙定向性明显;平均孔径及平均孔隙体积呈逐渐减小趋势;结构性原状土比表面积逐渐增大,重塑土则呈减小趋势;结构性原状土颗粒与孔隙分数维呈减小趋势,但重塑土呈相反趋势。  相似文献   

FREQUENCY AND MAGNITUDE OF BEDLOAD TRANSPORT IN A MOUNTAIN RIVER     

DOROTHEA GINTZ  MARWAN A. HASSAN  KARL-HEINZ SCHMIDT 《地球表面变化过程与地形》1996,21(5):433-445

Magnitude and frequency of bedload transport was examined in the Lainbach River, Bavaria, using magnetically tagged particles. During the study, 18 small to moderate events and one major event occurred. About 1 per cent of the flow period exceeded the entrainment threshold and at least once every year about 50 per cent of the tagged particles were mobile. Themajor event which occurred during the study period resulted in the deposition of a thick layer of sediment in parts of the channel and passive burial of most of the recovered particles. The step–pool pattern, which characterized the study site prior to the large event, was obliterated. However, the channel recovered quickly and has returned to a new step–pool pattern. The event changed the boundary conditions by increasing the availability of loose sediment and creating higher river-bed slopes in reaches between breached check dams. As a result, movement of individual particles measured for events of both the same magnitude and duration, occurring before and after the large event, yielded different values. For events which occurred after the large event, the range and the mean distance of movement were about ten times higher.  相似文献   

巢湖的稀土元素地球化学特征   总被引：2，自引：1，他引：1  

朱兆洲  王中良  高博  王仕禄 《地球化学》2006,35(6):639-644

采用液-液萃取法和ICP-MS测试技术对巢湖的溶解态稀土元素进行了分析。结果表明,巢湖的溶解态稀土的含量与世界淡水相当,丰水期的样品含量高于其他季节。pH值和悬浮物、胶体是控制巢湖水体中溶解态稀土含量的主要因素。巢湖的溶解态稀土的分布模式以平坦型为主,少数呈现重稀土富集。丰水期和枯水期的溶解态稀土的(La/Yb)N值从西半湖区到东半湖区呈现有规律性的逐渐增大,并且丰水期的(La/Yb)N值低于枯水期。在富营养化湖泊中,胶体和水生生物可能是造成这一现象的主要原因。  相似文献   

Acceleration time-scale in an ultrarelativistic shock     

Janusz Bednarz 《Monthly notices of the Royal Astronomical Society》2000,315(3):L37-L40

The acceleration mechanism in ultrarelativistic shocks is investigated using Monte Carlo simulations. We apply a method of discrete small-amplitude particle momentum scattering to reproduce highly anisotropic conditions at the shock and describe the acceleration mechanism carefully. The obtained acceleration time equals 1.0 r _g c if the spectral index reaches the value of 2.2, independent of physical conditions in the shock. Some other parameters of the acceleration process are also provided.  相似文献