Effective macroscopic transport parameters between parallel plates with constant concentration boundaries     

D.R. Webster  D.S. FeltonJ. Luo 《Advances in water resources》2007

A macroscopic transport model is developed, following the Taylor shear dispersion analysis procedure, for a 2D laminar shear flow between parallel plates possessing a constant specified concentration. This idealized geometry models flow with contaminant dissolution at pore-scale in a contaminant source zone and flow in a rock fracture with dissolving walls. We upscale a macroscopic transient transport model with effective transport coefficients of mean velocity, macroscopic dispersion, and first-order mass transfer rate. To validate the macroscopic model the mean concentration, covariance, and wall concentration gradient are compared to the results of numerical simulations of the advection–diffusion equation and the Graetz solution. Results indicate that in the presence of local-scale variations and constant concentration boundaries, the upscaled mean velocity and macrodispersion coefficient differ from those of the Taylor–Aris dispersion, and the mass transfer flux described by the first-order mass transfer model is larger than the diffusive mass flux from the constant wall. In addition, the upscaled first-order mass transfer coefficient in the macroscopic model depends only on the plate gap and diffusion coefficient. Therefore, the upscaled first-order mass transfer coefficient is independent of the mean velocity and travel distance, leading to a constant pore-scale Sherwood number of 12. By contrast, the effective Sherwood number determined by the diffusive mass flux is a function of the Peclet number for small Peclet number, and approaches a constant of 10.3 for large Peclet number.  相似文献   

The High Concentration Tails Of The Probability Density Function Of A Dispersing Scalar In The Atmosphere   总被引：1，自引：0，他引：1  

R. J. Munro  P. C. Chatwin  N. Mole 《Boundary-Layer Meteorology》2001,98(2):315-339

The distribution function for concentrations of a scalar pollutant dispersing in the turbulent atmosphere has a finite domain that is bounded above and below. Three methods, based on extreme value statistics, are used to obtainestimates for the upper bound and to describe the high concentration tailbehaviour of the distribution; all three methods are applied to concentrationdata obtained from experimental atmospheric releases. Quantile quantile (QQ)plots are used to assess the goodness of fit of the resulting estimates of thedistribution, and also to compare the performance of the three methods. Thepredicted values for the upper bound are orders of magnitude less than thesource concentration, illustrating that molecular diffusion has a large effecton the high concentrations.  相似文献   

地震面波产生的地震动转动分量研究   总被引：7，自引：0，他引：7  

李宏男  孙立晔 《地震工程与工程振动》2001,21(1):15-23

本文利用弹性波动理论对地面转动分量，即瑞利（Rayleigh)波和乐夫（Love)波产生的转动分量进行了研究，给出了相应的计算公式和计算方法，特别注意到面波的散射效应对转动分量的影响，并将这一特性引入到转动分量的求取中，使问题的解决更切合于实际，最后选取实际地震记录，利用得到的公式计算出地震面波产生的转动分量。  相似文献   

Health Risks and Environmental Inequity: A Geographical Analysis of Accidental Releases of Hazardous Materials     

Florence Lansana Margai 《The Professional geographer》2001,53(3):422-434

This study examines the spatial distribution and impact of nonroutine accidental releases of hazardous materials relative to the demographic composition of residents in nearby communities. First, atmospheric dispersion modeling methods are used to delineate the impact zones of worst‐case accidents in two New York counties over the last ten years. Next, using accidental reports for 1997, GIS and statistical operations are used at the census tract level of the two counties to determine whether these incidents disproportionately affected disadvantaged neighborhoods. The results suggest that the areas of high‐impact from accidental releases of hazardous materials are best characterized by a large proportion of families below the poverty line, Hispanics, and other minorities.  相似文献   

Normal Point Algorithm For Reduction Of Two Colour Slr Observations     

Stefan Riepl  Wolfgang Schlüter 《Surveys in Geophysics》2001,22(5-6):581-588

Two colour laser ranging to artificial satellites is an attractivetechnique, which is capable to provide refraction corrected ranges without the need of an atmospheric model by measuring the dispersive delay of laser pulses of different wavelength. Although the required accuracy of the detection scheme is stringent, the technique has matured so far, that routine two colour observationsbecame feasible.The present paper describes a normal point procedure reducing two colour laser range observations with respect to the dispersive delay,exploiting the knowledge of satellite response signatures in conjunction with detector characteristics and the appropriate center of mass correction models.Moreover the dispersion model of the atmosphere is briefly reviewed, paying attention to the wavelength domains provided by modern twocolour ranging lasers, e.g., the Ti:SAP laser.Preliminary data is presented and compared to both, normal point data reduced with a standard procedure and zenith path equivalent meteorological parameters.  相似文献   

THE FOUNDATION AND MOVEMENT OF TROPICAL SEMI-GEOSTROPHIC ADAPTATION   总被引：4，自引：0，他引：4       下载免费PDF全文

Chao Jiping  Lin Yonghui 《Acta Meteorologica Sinica》1996,10(2):129-141

The breakdown and foundation of geostrophic balance is one of the important movements inthe mid-and high-latitude atmosphere and oceans.In the tropical area,the value of Coriolis pa-rameter is so small that it is difficult to satisfy the bi-geostrophic equilibrium between the pressureand velocity fields.However,in the tropical area,the zonal velocity of some motions in the atmo-sphere and oceans is large,so the Coriolis force is not small,geostrophic balance can exist in zonaldirection,i.e.semi-geostrophic balance.Furthermore,in the dominant area of Hadley circulationin the atmosphere or the area near the ocean meridional boundary,the meridional velocity is large,so geostrophic balance can also exist in meridional direction.In this paper,the process of the dis-persion of inertial gravity wave and the foundation of semi-geostrophic balance are first discussed.Second,the adjustment process between the velocity and pressure fields after adaptation is alsoviewed,and the scale criterion of the semi-geostrophic adaptation is discussed,i.e.for the motionwith meridional scale greater than the equatorial Rossby radius of deformation,the velocity andpressure fields after adaptation change to fit the initial pressure field;on the contrary,the fieldschange to fit the initial zonal velocity field,and the strength of the fields after adaptation dependson the zonal scale.  相似文献   

高分辨区域输送模式中不同输送格式的对比试验   总被引：3，自引：0，他引：3  

葛孝贞  J.S. Chang  雷孝恩 《大气科学》1996,20(1):37-46

本文对两种输送格式在理论试验的基础上，引入19层高分辨区域输送模式EM3，由中尺度模式（MM4)提供实例输送风场，积分至13、18、30、50、70小时，作分析和对比数值试验。采用的两种格式是:二阶动量矩守恒的Prather格式（以下简称为SOM)及通量订正的Smolar格式。数值试验结果表明，高精度的SOM格式使数值扩散减小一个量级， 使输送物质（SO#-[2])中心浓度比Smolar格式增大3～4倍， 采用SOM格式还明显改进了浓度中心水平平均运动轨迹的模拟精度，选择高精度的平流格式是改进模拟结果的重要途径。  相似文献   

Modifications of the dispersion relations for surface waves in a layer on a half-space     

Oldřich Novotný  L. V. Burlako  T. A. Proskuryakova 《Studia Geophysica et Geodaetica》1996,40(2):167-177

Summary Dispersion relations for Love and Rayleigh waves in a layer on a half-space are modified by introducing quadratic slownesses instead of velocities. The advantages of this approach are demonstrated on analytical formulae for computing the group velocity.  相似文献   

Contamination of a well in a uniform background flow     

C. J. van der Hoek 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(3):191-207

In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed.  相似文献   

Propagation of surface waves on a laterally heterogeneous earth: asymptotic solution of the two-dimensional wave equation     

Fred F. Pollitz 《Geophysical Journal International》1992,111(1):67-78

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