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排序方式: 共有247条查询结果,搜索用时 31 毫秒
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73.
Liton Kumar SARKER M. Monowar HOSSAIN M. Anisul HAQUE 《国际泥沙研究》2007,22(3):169-179
Experiments on initiation of motion of different fractions of non-uniform sediment mixtures are reported. Four sediment mixes and reference transport method to define the threshold of bed particle movement are used in this analysis. Factors controlling the initiation of motion are analyzed. It is found that relative size of different grains with respect to a median size greatly affects the initiation of movement. The incipient motion of non-uniform sediment is very much dependent on the absolute size for coarser fractions. Considering the factors controlling the initiation of motion the experimental data sets along with the other available data yield a new relationship for the calculation of critical shear stress of non-uniform sediments. A set of equations have found that all the data points fall into a single line for the finer and for coarser fractions. 相似文献
74.
Danièle Valdes Jean-Paul Dupont Nicolas Massei Benoît Laignel Joël Rodet 《Comptes Rendus Geoscience》2005,337(15):1365-1374
In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005). 相似文献
75.
It is essential to learn the temporal and spatial concentration distributions and variations of seeding agents in cloud seeding
of precipitation enhancement. A three–dimensional puff trajectory model incorporating a mesoscale nonhydrostatic model has
been formulated, and is applied to simulating the transporting and diffusive characteristics of multiple line sources of seeding
agents within super–cooled stratus. Several important factors are taken into consideration that affect the diffusion of seeding
materials such as effects of topography and vertical wind shear, temporal and spatial variation of seeding parameters and
wet deposition. The particles of seeding agents are assumed to be almost inert, they have no interaction with the particles
of the cloud or precipitation except that they are washed out by precipitation. The model validity is demonstrated by the
analyses and comparisons of model results, and checked by the sensitivity experiments of diffusive coefficients and atmospheric
stratification. The advantage of this model includes not only its exact reflection of heterogeneity and unsteadiness of background
fields, but also its good simulation of transport and diffusion of multiple line sources.
The horizontal diffusion rate and the horizontal transport distance have been proposed that they usually were difficult to
obtain in other models. In this simulation the horizontal diffusion rate is 0.82 m s−1 for average of one hour, and the horizontal average transport distance reaches 65 km after 1 h, which are closely related
to the background fields. 相似文献
76.
利用INSTANT(The International Nusantara Stratification and Transport,努沙登加拉层结及输运的国际联合观测计划)计划所测得的流场数据,研究了ITF(Indonesian Throughflow,印度尼西亚贯穿流)在主要流出海峡——龙目海峡(Lombok Strait)、翁拜海峡(Ombai Strait)和帝汶海峡(Timor Passage)随深度和时间的变化,并对表层和温跃层的流速进行了功率谱分析。研究发现,ITF流场在龙目和翁拜海峡表层有显著的年循环,在季风转换期间各个层次上海流都会出现反转,从印度洋流向海峡内;而帝汶海峡在300m以下出现反转流。3个海峡的表层流都以年周期为主,温跃层的流以半年变化为主,并且都有丰富的季节内变化。高频部分,除了在龙目海峡表层K1日潮占优外,各海峡均以M2半日潮为主。 相似文献
77.
迁移方程在原子核物理、气象预报和人口理论等方面具有广泛的应用,此类问题的逆问题更具有其实用性。作者在已有工作的基础上,应用奇异积分方程理论,给出了求解此类问题的具体表达式。 相似文献
78.
Ephemeral channels in arid regions convey larger amounts of sediment than perennial channels in humid regions. Sediment graphs at the outlet of channels have been derived by the standard sediment rating curve technique and by a lumped model based on the instantaneous unit sediment graph (IUSG) concept. The IUSG gives estimates of sediment transport that are better than those derived with the sediment rating curve as it takes into account the availability of erodible material within the channel bed. 相似文献
79.
《Comptes Rendus Geoscience》2014,346(9-10):255-261
We studied the transport of a pesticide at field scale, namely carbofuran molecule, which is known for its high mobility, especially in sandy soils with high hydraulic conductivity and low organic matter. To add to our knowledge of the future of this high-mobility molecule in this type of soils, we developed a mechanistic numerical model allowing the simulation of hydric and solute transfers (bromide and carbofuran) in the soil. We carried out this study in an agricultural plot in the region of Mnasra in Morocco. Confrontation of the measured and simulated values allowed the calibration of the parameters of hydric transfer and carbofuran. The developed model accurately reproduces the measured values. Despite a weak irrigation and precipitation regime, carbofuran was practically leached beyond the root zone. Prospective simulations show that under a more important irrigation regime, carbofuran reaches a 100-cm depth, whereas it does not exceed 60 cm under a deficit regime. 相似文献
80.
《Comptes Rendus Geoscience》2014,346(1-2):37-44
We document the sedimentary facies of a large Mass Transport Deposit (MTD) within the sand-rich sediment gravity flow-dominated deposits of the Eocene–Oligocene south-western Alpine forelands (Annot Sandstone system). The MTD with an approximated volume of several hundreds of cubic kilometres fills a sub-basin located in the Mont-Tournairet confined sub-basin. Autochthonous facies are very typical sediment gravity-flow deposits (thin-bedded classical turbidites and thick-bedded hyperconcentrated to concentrated flow deposits) that stratigraphically belong to the Annot Sandstone infill. Slumps and internal metre-large fold axes of the deformed stratigraphic intervals indicate a main transport direction towards the northwest. The seafloor instability that led to the mass-flow events within the Mont-Tournairet sub-basin could have been favoured by high sedimentation rates in a small, confined and tectonically active sub-basin, possibly enhanced by local structural deformation associated with the Triassic evaporites on the eastern side of the Mont-Tournairet confined basin. The presence of the MTD suggests that a period of increased flexural subsidence rate and basin deformation occurred in this portion of the subalpine foreland basin. Therefore, the MTD forms a stratigraphic marker of a period of tectonic activity. 相似文献