IAP AGCM中短波辐射方案的改进研究II·短波辐射方案的改进     

张凤  曾庆存 《气候与环境研究》2005,(3)

在Version 2的基础上,对短波辐射方案进行进一步的改进:引入了新增非灰体气体吸收效应、冰晶粒子形状效应和尺度效应以及云的不均匀性效应(称为Version 3)。数值模拟试验结果表明:Version 3能更好地模拟出全球冬、夏季的降水场、海平面气压场及地表气温场的主要分布特征,并且能相当准确地反映出这几个场的季节性变化特征。Version 3对这3个场的模拟能力明显优于原版本(Version 1)。此外,它对东亚地区的季风降雨具有很好的模拟能力,能较好地反映东亚区域降水的季节性变化。可见,Version 3为进一步研究云-辐射相互作用提供了很好的模式基础。本工作还清楚地表明,模式的进一步发展必须进行对相关物理过程中各个因子的更精确刻画,只有这样,模式才能得到更好的模拟能力。  相似文献   

Three-dimensional petrographical investigations on borehole rock samples: a comparison between X-ray computed- and neutron tomography     

P. Christe  M. Bernasconi  P. Vontobel  P. Turberg  A. Parriaux 《Acta Geotechnica》2007,2(4):269-279

Technical difficulties associated with excavation works in tectonized geological settings are frequent. They comprise instantaneous and/or delayed convergence, sudden collapse of gallery roof and/or walls, outpouring of fault-filling materials and water inflows. These phenomena have a negative impact on construction sites and their safety. In order to optimize project success, preliminary studies on the reliability of rock material found on site are needed. This implies in situ investigations (surface mapping, prospective drilling, waterflow survey, etc.) as well as laboratory investigations on rock samples (permeability determination, moisture and water content, mineralogy, petrography, geochemistry, mechanical deformation tests, etc.). A set of multiple parameters are then recorded which permit better insight on site conditions and probable behavior during excavation. Because rock formations are by nature heterogeneous, many uncertainties remain when extrapolating large-scale behavior of the rock mass from analyses of samples order of magnitudes smaller. Indirect large-scale field investigations (e.g. geophysical prospecting) could help to better constrain the relationships between lithologies at depth. At a much smaller scale, indirect analytical methods are becoming more widely used for material investigations. We discuss in this paper X-ray computed tomography (XRCT) and neutron tomography (NT), showing promising results for 3D petrographical investigations of the internal structure of opaque materials. Both techniques record contrasts inside a sample, which can be interpreted and quantified in terms of heterogeneity. This approach has the advantage of combining genetic parameters (physico-chemical rock composition) with geometric parameters resulting from alteration or deformation processes (texture and structure). A critical analysis of such 3D analyses together with the results of mechanical tests could improve predictions of short- and long-term behavior of a rock unit. Indirect methods have the advantage of being non-destructive. However, as it is the case with large-scale geophysical surveying, XRCT and NT are affected by several error factors inherent to the interaction of a radiation modality (X-ray or neutron beam) with the atomic structure of the investigated materials. Recorded signals are therefore in particular cases not artifact-free and need to be corrected in a subsequent stage of data processing.  相似文献   

NUMERICAL STUDY ON THE MIXING OF UNSORTED SEDIMENT PARTICLES DISCHARGED INTO A CROSS-FLOW BY MULTIPHASE PARTICLE-IN-CELL （MP-PIC） METHOD     

Jie GU Chiwai LI Hong YANG Yong ZHAN 《国际泥沙研究》2007,22(2):150-159

The mixing characteristics of dredged sediments of variable size discharged into cross-flow are studied by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model has been developed by using the modified k-ε parameterization for the turbulence in fluid phase/water and a Lagrangian method for the solid phase/sediments. In the model the wake turbulence induced by sediments has been included as additional source and sink terms in the k-ε model; and the trajectories of the sediments are tracked by the Lagrangian method in which the sediment drift velocities in cross-flow are computed by a multiphase particle-in-cell (MP-PIC) method and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumped sediment cloud is governed by the total buoyancy on the cloud, the drag force on each particle and velocity of cross-flow. The cross-flow destroys more or less the double vortices occurred in stagnant ambience and dominates the longitudinal movement of sediment cloud. The computed results suggest satisfactory agreement by comparison with the experimental results of laboratory.  相似文献   

The fate of inorganic colloidal particles in Lake Brienz     

Vincent Chanudet  Montserrat Filella 《Aquatic Sciences - Research Across Boundaries》2007,69(2):199-211

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Approaches for modeling longitudinal dispersion in pore-networks     

R.C. Acharya  S.E.A.T.M. Van der Zee  A. Leijnse 《Advances in water resources》2007

The purpose of this study is to quantify the dispersivity in the longitudinal direction by upscaling pore scale mixing over a network domain and to verify the dispersivity with that obtained through the more rigorous upscaling technique, the Brownian particle tracking model (BPTM). We model a porous medium with a network of pore-units that are comprised of pore bodies and bonds of finite volume. Such a pore-unit is assumed to be a mixing cell with the steady state flow condition for a single fluid. Dispersivity can be obtained by solving the mixing cell model (MCM) for the concentration in each pore-unit and by averaging the concentrations for a large number of pore units (as a function of time and space). A minimal size of network that ascertains an asymptotic value of dispersivity was determined and verified with large size pore networks. This numerically computed dispersivity is compared with the results from the BPTM for the same porous medium and flow conditions. We show that the dispersivity obtained from the MCM is equally reliable for the heterogeneous pore-networks and can be estimated as a function of pore size heterogeneity. For homogeneous networks with the MCM, the iteration time step plays an important role. On the other hand, for networks with the BPTM, the assumption of intra-bond velocity profile affects the results.  相似文献   

Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles     

Tony Wells  Garry Willgoose  Philip Binning 《地球表面变化过程与地形》2007,32(5):687-697

Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Pb and Th in settling particles in the western Northwest Pacific Ocean: Particle flux and scavenging     

Masatoshi Yamada  Jian Zheng 《Continental Shelf Research》2007

A mooring of three conical time-series sediment traps was deployed at two sites in the western Northwest Pacific Ocean for 9 months. Total mass fluxes and activities of ²¹⁰Pb and ²³⁰Th were determined for the settling particles to elucidate their scavenging and transport processes. Sediment samples also were analyzed for ²¹⁰Pb activities. Total mass fluxes, ²¹⁰Pb fluxes and ²³⁰Th fluxes showed large seasonal variations and their weighted mean fluxes tended to increase with depth, with an especially large increase near-bottom. The ratios of the observed ²¹⁰Pb fluxes to the ²¹⁰Pb deficiency fluxes in the upper traps at the two sites were only 0.02 and 0.12, and were attributable to advective export of ²¹⁰Pb from the surface waters. Those ratios in the near-bottom traps ranged between 1.22 and 2.63. This suggests that these high ratios are due to effective particle scavenging, large lateral ²¹⁰Pb import and input of resuspended particles that have not become incorporated into the sediments. The mean total ²³⁰Th fluxes at the near-bottom traps were 4.2–6.7 times higher than that expected from production in the overlying water column. The ²¹⁰Pb activities in the surficial sediments were much lower than those in the near-bottom traps. The ²¹⁰Pb accumulation rates estimated from the excess ²¹⁰Pb inventory in the sediment column were 40–70% higher than the mean ²¹⁰Pb fluxes at the near-bottom traps. The ratios of the ²¹⁰Pb accumulation rates to the ²¹⁰Pb deficiency fluxes at the near-bottom traps ranged between 2.0 and 3.7. The high fluxes of particulate ²¹⁰Pb and ²³⁰Th at the near-bottom traps reflected a combination of enhanced scavenging of dissolved nuclides and the lateral redistribution of particulate matter by downslope and alongshore transports. However, it was not possible to discriminate among the various processes contributing to high nuclide fluxes.  相似文献   

非定常不稳定液固两相流动中旋涡对颗粒运动影响的数值研究   总被引：2，自引：0，他引：2       下载免费PDF全文

黄远东  吴文权  张红武  王光谦 《水科学进展》2002,13(1):1-8

构建起双向耦合的液固两相流动旋涡动力学模型与数值方法;应用离散涡方法,计算非定常不稳定水流场;采用Lagrange方法模拟颗粒运动,颗粒对流体的反作用通过修正涡泡运动速度来实现。利用所建模型,计算了两种St数的泥沙粒子在圆柱绕流场中的运动。结果证明了液固两相流动中颗粒运动与旋涡存在着明确的相关结构:(1)当水沙混合物中的泥沙颗粒碰上旋涡时,泥沙颗粒被卷入旋涡中,被卷入旋涡中的泥沙颗粒在运动过程中始终分布于旋涡区;(2)均匀水沙混合物绕圆柱流动,由于流体流过圆柱时产生剧烈分离流动,使得在尾迹流内中等St数 (St～o (1))的泥沙颗粒从均匀水沙混合物中分离出来而往旋涡区聚集。  相似文献   

四川紫色雏形土的蒸发性及其与土壤结构性的关系     

宫阿都  何毓蓉 《山地学报》2001,(Z1)

结合四川土壤基层分类 ,选取四川紫色雏形土的几个土系 ,对土壤的水分发性能及其与土壤结构性尤其是机械组成和微团聚体组成的相关关系分析发展 ,土壤水分蒸发具有明显的阶段性 ;土壤水分累积蒸发量与蒸发历时之间总体上符合乘幂方程 ;土壤蒸发速度与〈0 .0 0 1mm的颗粒含量呈明显相关关系 ,与 >0 .2 5mm的大团聚体含量呈明显负相关关系。  相似文献   

含粘粒砂土抗液化性能的试验研究   总被引：20，自引：1，他引：20  

衡朝阳  何满潮  裘以惠 《工程地质学报》2001,9(4):339-344

通过对含粘粒砂土所作的试验研究, 包括: 粘粒矿物成分不同、粘粒含量不同的重塑土样所作的室内动三轴试验; X光衍射试验, 试验结果对比分析后, 得出了含粘粒砂土抗液化性能的特性。并得出以下结论: (1)粘粒矿物成分不同, 也引起砂土动力稳定性的变化; (2 )动剪应力强度与粘粒含量并非呈单调增加关系, 而呈抛物线型, 并给出回归方程; (3)含粘粒的砂土, 其抗液化能力最低点总是在粘粒含量 8.5～ 9.5 %之间。  相似文献