Variable-density flow and transport in porous media: approaches and challenges     

H.-J.G. Diersch  O. Kolditz 《Advances in water resources》2002,25(8-12)

We review the state of the art in modeling of variable-density flow and transport in porous media, including conceptual models for convection systems, governing balance equations, phenomenological laws, constitutive relations for fluid density and viscosity, and numerical methods for solving the resulting nonlinear multifield problems. The discussion of numerical methods addresses strategies for solving the coupled spatio-temporal convection process, consistent velocity approximation, and error-based mesh adaptation techniques. As numerical models for those nonlinear systems must be carefully verified in appropriate tests, we discuss weaknesses and inconsistencies of current model-verification methods as well as benchmark solutions. We give examples of field-related applications to illustrate specific challenges of further research, where heterogeneities and large scales are important.  相似文献   

Molecular dynamics modeling of stishovite     

Sheng-Nian Luo  Tahir Ça?inAlejandro Strachan  William A. Goddard IIIThomas J. Ahrens 《Earth and Planetary Science Letters》2002,202(1):147-157

A Morse-stretch potential charge equilibrium force field for silica system has been employed to simulate the thermodynamics of stishovite with the molecular dynamics (MD) method. The equation of state, thermal expansivity and melting curve of stishovite have been obtained. This simple force field yielded results in accordance with the static and dynamic experiments. The stishovite melting simulation appears to validate the interpretation of superheating of the solid along the Hugoniot in the shock melting experiments. MD simulations show that the thermal expansivity of stishovite at lowermost mantle conditions is a weak function of temperature. The phase diagram of silica up to the mega bar regime is proposed based on the experimental and theoretical studies. The related physical and geophysical implications are addressed.  相似文献   

Tag retention and survival of fish tagged in controlled pond experiments     

Wiesław Wiśniewolski  Jerzy Nabiałek 《Aquatic Sciences - Research Across Boundaries》1993,55(2):143-152

Fish survival, tag retention and tag loss were evaluated in pond experiments and described by linear regression equations. Tagging of fish had no significant influence on their survival. However, loss of tags caused strong differences between actual fish survival and the survival rate e^–z estimated on recovered tags. Mathematical functions were derived to correct tag loss. Values of those functions depend upon the type of tag and time after tagging. The B-type of tagging, which approximated the Swedish Carlin method, appeared to be most effective. The rate of tag loss was independent of the fish species (common carp, tench) used in the experiments.  相似文献   

Thermodynamic Properties of Brucite Determined by Solubility Studies and Their Significance to Nuclear Waste Isolation     

Yongliang Xiong 《Aquatic Geochemistry》2008,14(3):223-238

Solubility experiments were conducted for the dissolution reaction of brucite, Mg(OH)₂ (cr): Experiments were conducted from undersaturation in deionized (DI) water and 0.010–4.4 m NaCl solutions at 22.5°C. In addition, brucite solubility was measured from supersaturation in an experiment in which brucite was precipitated via dropwise addition of 0.10 m NaOH into a 0.10 m MgCl₂ solution also at 22.5°C. The attainment of the reversal in equilibrium was demonstrated in this study. The solubility constant at 22.5°C at infinite dilution calculated from the experimental results from the direction of supersaturation by using the specific interaction theory (SIT) is: with a corresponding value of 17.0 ± 0.2 (2σ) when extrapolated to 25°C. The dimensionless standard chemical potential (μ°/RT) of brucite derived from the solubility data in 0.010 m to 4.4 m NaCl solutions from undersaturation extrapolated to 25°C is −335.76 ± 0.45 (2σ), with the corresponding Gibbs free energy of formation of brucite, , being −832.3 ± 1.1 (2σ) kJ mol⁻¹. In combination with the auxiliary thermodynamic data, the is calculated to be 17.1 ± 0.2 (2σ), based on the above Gibbs free energy of formation for brucite. This study recommends an average value of 17.05 ± 0.2 in logarithmic unit as solubility constant of brucite at 25°C, according to the values from both supersaturation and undersaturation. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.  相似文献   

直线方程在工程测量中的运用     

翟警卫 《测绘与空间地理信息》2008,31(6)

通过实例,介绍一种在工程测量中从某一已知点上放样直线或直线上任意点确定其平面位置和高程位置的方法.此方法既可提高工作效率和放样精度,又能满足工程测量的需要.  相似文献   

Alternative forms of the higher-order Boussinesq equations: Derivations and validations   总被引：2，自引：0，他引：2  

Z.L. Zou  K.Z. Fang 《Coastal Engineering》2008

An alternative form of the Boussinesq equations is developed, creating a model which is fully nonlinear up to O(μ⁴) (μ is the ratio of water depth to wavelength) and has dispersion accurate to the Padé [4,4] approximation. No limitation is imposed on the bottom slope; the variable distance between free surface and sea bottom is accounted for by a σ-transformation. Two reduced forms of the model are also presented, which simplify O(μ⁴) terms using the assumption ε = O(μ^2/3) (ε is the ratio of wave height to water depth). These can be seen as extensions of Serre's equations, with dispersions given by the Padé [2,2] and Padé [4,4] approximations. The third-order nonlinear characteristics of these three models are discussed using Fourier analysis, and compared to other high-order formulations of the Boussinesq equations. The models are validated against experimental measurements of wave propagation over a submerged breakwater. Finally, the nonlinear evolution of wave groups along a horizontal flume is simulated and compared to experimental data in order to investigate the effects of the amplitude dispersion and the four-wave resonant interaction.  相似文献   

Numerical modelling of dynamic consolidation on granular soils     

S. López‐Querol  J. A. Fernández‐Merodo  P. Mira  M. Pastor 《国际地质力学数值与分析法杂志》2008,32(12):1431-1457

The application of Pastor–Zienkiewicz constitutive model for sands to dynamic consolidation problems is presented in this paper. This model is implemented in a coupled code formulated in terms of displacements for both solid and fluid phases (u?w formulation), which is firstly compared with u?p_w formulation for some simple examples. Its range of validity, previously established for elastic problems and harmonic loading, is explored. Once the suitability of the u?w formulation has been ascertained for this kind of dynamic problems in soils, one‐ and two‐dimensional (plane strain) dynamic consolidation numerical examples are provided, aiming to give some light into the physics of this ground improvement technique. A ‘wave of dryness’, observed at the soil surface during the impact in field cases, is numerically reproduced and justified. Some hints on the influence of the loading zone size are also given. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Simulation of Random Waves and Associated Laminar Bottom Shear Stresses     

Mao-Lin SHEN  Ching-Jer HUANG 《中国海洋工程》2008,22(3):477-490

This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.  相似文献   

海浪感应电磁场的理论计算   总被引：4，自引：0，他引：4       下载免费PDF全文

张自力  魏文博  刘保华  邓明  金胜 《海洋学报》2008,30(1):42-46

根据麦克斯韦电磁理论,在地磁场中运动的海水将产生感应电磁场。利用一个简单的数学物理模型对感应电磁场在海水内部的分布进行了计算,结果表明海浪产生的电磁场明显依赖于海浪波动的周期及浪高。在100 m的海水深度内,海浪产生的磁感应强度的大小为纳特数量级,而电场强度的大小为几个微伏每米。在同一海水深度处,磁感应强度随海水波动的周期呈现近线性变化,而电场强度的大小有一个极值,该极值随海水深度的增加向长周期方向移动。海浪产生的电磁场是影响海洋电磁探测数据精度的主要噪声之一。  相似文献   

Hyperbolic Mild Slope Equations with Inclusion of Amplitude Dispersion Effect: Random Waves     

ZOU Zhi-li  JIN Hong 《中国海洋工程》2008,22(4)

New hyperbolic mild slope equations for random waves are developed with the inclusion of amplitude dispersion. The frequency perturbation around the peak frequency of random waves is adopted to extend the equations for regular waves to random waves. The nonlinear effect of amplitude dispersion is incorporated approximately into the model by only considering the nonlinear effect on the carrier waves of random waves, which is done by introducing a representative wave amplitude for the carrier waves. The computation time is greatly saved by the introduction of the representative wave amplitude. The extension of the present model to breaking waves is also considered in order to apply the new equations to surf zone. The model is validated for random waves propagate over a shoal and in surf zone against measurements.  相似文献