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71.
Density-dependent dispersion in heterogeneous porous media Part I: A numerical study 总被引:1,自引:0,他引:1
In this paper, we describe carefully conducted numerical experiments, in which a dense salt solution vertically displaces fresh water in a stable manner. The two-dimensional porous media are weakly heterogeneous at a small scale. The purpose of these simulations, conducted for a range of density differences, is to obtain accurate concentration profiles that can be used to validate nonlinear models for high-concentration-gradient dispersion. In this part we focus on convergence of the computations, in numerical and statistical sense, to ensure that the uncertainty in the results is small enough.Concentration variances are computed, which give estimates of the uncertainty in local concentration values. These local variations decrease with increasing density contrast. For tracer transport, obtained longitudinal dispersivities are in accordance with analytical findings. In the case of high-density contrasts, stabilizing gravity forces counteract the growth of dispersive fingers, decreasing the effective width of the transition zone. For small log-permeability variances, the decrease of the apparent dispersivity that is found is in agreement with laboratory results for homogeneous columns. 相似文献
72.
Application of bivariate extreme value distribution to flood frequency analysis: a case study of Northwestern Mexico 总被引:1,自引:0,他引:1
Carlos Escalante-Sandoval 《Natural Hazards》2007,42(1):37-46
In Mexico, poverty has forced people to live almost on the water of rivers. This situation along with the occurrence of floods
is a serious problem for the local governments. In order to protect their lives and goods, it is very important to account
with a mathematical tool that may reduce the uncertainties in computing the design events for different return periods.
In this paper, the Logistic model for bivariate extreme value distribution with Weibull-2 and Mixed Weibull marginals is proposed
for the case of flood frequency analysis. A procedure to estimate their parameters based on the maximum likelihood method
is developed. A region in Northwestern Mexico with 16 gauging stations has been selected to apply the model and regional at-site
quantiles were estimated. A significant improvement occurs, measured through the use of a goodness-of-fit test, when parameters
are estimated using the bivariate distribution instead of its univariate counterpart. Results suggest that it is very important
to consider the Mixed Weibull distribution and its bivariate option when analyzing floods generated by a␣mixture of two populations. 相似文献
73.
根据国内外大量实际资料,从碘的分布情况及其所处的地质条件,结合石油和天然气形成过程、油气藏类型及其分布特点,探讨高碘卤水分布的规律及其形成条件,在此基础上指出了我国的找碘方向。 相似文献
74.
In this paper, we formulate a finite element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. Here, we approximate the pressure by a mixed finite element method and the displacements by a Galerkin
method. Theoretical convergence error estimates are derived in a discrete-in-time setting. Of particular interest is the case
when the lowest-order Raviart–Thomas approximating space or cell-centered finite differences are used in the mixed formulation
and continuous piecewise linear approximations are used for displacements. This approach appears to be the one most frequently
applied to existing reservoir engineering simulators. 相似文献
75.
In this paper, we formulate a finite element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. Here, we approximate the pressure by a mixed finite element method and the displacements by a Galerkin
method. Theoretical convergence error estimates are derived in a continuous in-time setting for a strictly positive constrained
specific storage coefficient. Of particular interest is the case when the lowest-order Raviart–Thomas approximating space
or cell-centered finite differences are used in the mixed formulation, and continuous piecewise linear approximations are
used for displacements. This approach appears to be the one most frequently applied to existing reservoir engineering simulators. 相似文献
76.
Building comparable global change vulnerability assessments: The vulnerability scoping diagram 总被引:29,自引:1,他引:29
Advancing vulnerability science depends in part on identifying common themes from multiple, independent vulnerability assessments. Such insights are difficult to produce when the assessments use dissimilar, often qualitative, measures. The Vulnerability Scoping Diagram is presented to facilitate the comparison of assessments with dissimilar measures. The diagram is illustrated with recent research on drought vulnerabilities, showing that common insights into vulnerability may emerge if independent research teams use a common structure for organizing information about exposure, sensitivity and adaptive capacity—even if the underlying measures differ between assessments. Broadly adopting this technique, which is grounded in the “Eight Steps” methodological protocol [Schröter, D., Polsky, C., Patt, A., 2005. Assessing vulnerabilities to the effects of global change: an eight step approach. Mitigation and Adaptation Strategies for Global Change 10(4), 573–595], will enable a vulnerability meta-analysis, the lessons from which may permit places to identify helpful adaptation or mitigation options without first having to conduct their own vulnerability assessments. 相似文献
77.
Wind tunnel experiments were carried out to measure the spatial distribution in equilibrium transport of four types of mixed sand. The flux profiles of each grain size group were calculated. It is found that the vertical distribution of mean grain size has a close relation with the grain size distribution in the sand bed. In a log-linear plot, the flux profiles of main grain size groups are all straight lines and their slopes are nearly equal. It is also found that the ratio of transport rate of each size group to the whole transport rate is directly proportional to the mass ratio of each size group in the sand bed and the proportion value is only dependent on the grain size. This harmonious law is applicable to all four types of mixed sand used in the experiment. 相似文献
78.
79.
根据国内外大量实际资料,从碘的分布情况及其所处的地质条件,结合石油和天然气形成过程、油气藏类型及其分布特点,探讨高碘卤水分布的规律及其形成条件,在此基础上指出了我国的找碘方向。 相似文献
80.