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排序方式: 共有668条查询结果,搜索用时 375 毫秒
91.
92.
通过综合利用ECMWF提供的热带风场、气压场、高度场等资料,对24例影响广西的热带气旋环境流场和一些物理量特征进行了较为深入的分析。结果表明:大多数热带气旋的发生、发展都与赤道西风急流向东扩展或热带气旋东侧南风急流向北扩展有关;造成广西大范围台风暴雨的因素不仅取决于台风登陆地点和登陆后的路径以及中心是否直接进入广西内陆有关,而且还与副热带高压脊线的位置和面积指数、强度指数的变化关系密切。登陆台风在影响广西的过程中,其台风东侧的偏南风急流中心涌进广西和正涡度中心进入广西对产生大范围的暴雨起着重要的作用。 相似文献
93.
Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2013,31(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
94.
定量分析碳酸盐岩孔洞型储集体的地震响应特征,对孔洞储集体的预测和刻画研究有着重要意义.基于声波方程,在忽略多次散射的情况下,导出了深层小尺度孤立洞体的地震响应近似解析式,该解析表达式给出了孔洞尺度、充填程度与地震振幅属性之间的关系.分析表明:(1)当孔洞异常体尺度小于地震波长的1/8时,反射波振幅与异常体体积呈近似正比关系;(2)异常体横向上的尺度对反射波振幅的影响主要由菲涅耳半径控制,同时振幅随横向尺度的变化规律受到纵向尺度的影响;(3)异常体纵向上的尺度对反射振幅的影响主要表现为调谐效应,当纵向上的尺度等于调谐厚度(地震波长的1/4)时,反射振幅最强.不同尺度溶洞的数值模拟研究结果以及不同填充物的单洞物理模型试验和溶洞群物理模型试验验证了以上结论的正确性. 相似文献
95.
The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral‐associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by 13C‐NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra‐macroaggregate SOM, which is then separated by density. Finally, intra‐microaggregate SOM is isolated from mineral‐associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral‐associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted‐aliphatic material, most probably lipid biopolymers. 相似文献
96.
97.
Faulting is one type of permanent ground displacement (PGD); tunnels are at the risk of damage when they are susceptible to faulting. The present study proposes an experimental approach to create the fragility curves for shallow segmental tunnels in alluvial deposits subjected to normal surface faulting. Centrifuge testing was carried out in order to achieve this purpose. The proposed approach allows evaluation of new fragility curves considering the distinctive features of tunnel geometry and fault specifications. The comparison between the new fragility curves and the existing empirical curves was discussed as well. Compared to tunnels in rock, tunnels in alluvial deposits are more susceptible to failure because of different mechanisms of collapse into tunnel at large exerted PGD. 相似文献
98.
岩体节理几何特征定量描述是岩体力学性质和渗透性研究的基础,更是核废料处置库场址筛选和评价过程的主要内容。基于甘肃北山高放废物深地质处置库预选区BS17、BS18和BS19钻孔岩芯节理数量修正数据,针对节理间距建立了类负指数分布数学统计模型,进一步应用于RQD体系定量评价深部岩体完整性,通过与RID体系对比验证了概率模型的可靠性。指出节理数量-间距关系具有明显的分段线性特征,分维数随着间距增大而增大。确定了节理间距-数量关系符合尺度律,得出了数量与间距关系的多重分形特征。进一步分析了数量与埋深的多重分形特征,初步实现了岩芯节理的定量描述。验证了多重分形谱可以很好地统计分形维特征,尤其是节理几何形状及分布特征。该研究结果可为实现基于钻孔岩芯节理几何特征数据的深部岩体节理三维网格模拟提供参考。 相似文献
99.
100.
Andres DIE MORAN Kamal EL KADI ABDERREZZAK Erik MOSSELMAN Helmut HABERSACK Franck LEBERT Denis AELBRECHT Eric LAPERROUSAZ 《国际泥沙研究》2013,28(4):431-447
A mobile-bed, undistorted physical model (1:40) has been used to investigate different sediment supply strategies to the Old Rhine through bank protection removal and modifications of groyne dimensions and configuration, which cause bank erosion. This trained channel was previously the main bed of the upper Rhine downstream of Basel (Switzerland), but it has an artificially low flow regime since the construction of the Grand Canal d'Alsace, a navigation canal, and a flow control dam at Kembs (France). Training works and subsequent channel incision have also greatly reduced sediment transport rates and created a heavily armoured bed. The modelled pilot site has a groyne field on the left bank. Results show that the currently existing groynes at the site are not effective in creating high bank-side velocities conducive to bank erosion, even for flow rates significantly higher than the mean annual flow rate. The river bank has also proved to be more resistant than previously thought, allowing long stretches of bank protection to be safely removed. The physical model testing process has produced a new configuration for the groyne field, where two higher, larger island groynes are placed further apart than the three existing attached groynes. This innovative approach has proved effective, causing bank erosion for flow rates below the mean annual flow rate, with consistent erosion being observed. It has also been found that such a configuration does not pose a hazard for the Grand Canal d'Alsace, which is situated next to the Old Rhine, through excessive bank erosion during high flow events. 相似文献