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  • coefficient of variation  (1)
  • fluctuations  (1)
  • Springer  (2)
  • 1995-1999  (2)
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  • Springer  (2)
Years
  • 1995-1999  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Advection-diffusion in spatially random flows: Formulation of concentration covariance (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 397-422 
    Details
    ISSN: 1436-3259
    Keywords: Random flow field ; diffusion ; concentration ; fluctuations ; covariance ; variance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The concentration c(x,t) of a nonreactive solute undergoing advection and diffusion in a spatially random divergence-free flow field is analyzed. A leading order formulation for the spatial covariance of the concentration field, $$\overline {c'\left( {x,t} \right)c'\left( {x,t} \right)} $$ , is made. That formulation includes the velocity variability induced macrodispersive flux of the covariance field, and the smoothing effects of diffusion. Previous formulations of the concentration covariance had dropped at least one of these effects. It is shown that both these effects need to be included to obtain a qualitatively correct description of the concentration fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427926
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  • 2
    Electronic Resource
    Electronic Resource
    Concentration fluctuations and dilution in two-dimensionally periodic heterogeneous porous media (1996)
    Springer
    Transport in porous media 22 (1996), S. 91-119 
    Details
    ISSN: 1573-1634
    Keywords: concentration fluctuations ; peak concentration ; dilution ; heterogeneity ; local dispersion ; microscale ; fluctuation dissipation ; coefficient of variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Dilution of solute in two-dimensionally periodic heterogeneous porous media is assessed by numerically simulating advection-dispersion. The concentration fluctuations, created by advective heterogeneity, are destroyed by local dispersion, over a characteristic variance residence time (VRT). For an impulse introduction of solute, initially, plumes become increasingly irregular with time—the coefficient of variation (CV) of concentration grows with time. A priori, the spatial second moment and mean concentrations are insufficient measures of dilution, because concentration fluctuations can be large. At large times (t 〉 VRT) the relative concentration fluctuations weaken—the concentration CV was observed to slowly decrease with time. At the center of mass the general trend of the decreasing CV follows VRT/t (predicted by Kapoor and Gelhar). The VRT is found to be an increasing function of the log hydraulic conductivity microscale. In employing effective dispersion coefficents to model the mean concentration, it needs to be recognized that excursions of concentrations around the mean are singularly determined by local dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00974313
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