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@ARTICLE{Bechtold:17041,
      author       = {Bechtold, M. and Vanderborght, J. and Ippisch, O. and
                      Vereecken, H.},
      title        = {{E}fficient random walk particle tracking algorithm for
                      advective dispersive transport in media with discontinuous
                      dispersion coefficients and water contents},
      journal      = {Water resources research},
      volume       = {47},
      issn         = {0043-1397},
      address      = {Washington, DC},
      publisher    = {AGU},
      reportid     = {PreJuSER-17041},
      pages        = {W10526},
      year         = {2011},
      note         = {This study was funded by the network EOS
                      (www.netzwerk-eos.dlr.de). We thank Horst Hardelauf who
                      coupled the finite volume flow code to the PARTRACE code and
                      Michael Herbst for the introduction to the PARTRACE code. We
                      thank Colin Kikuchi for his help in improving the English
                      wording.},
      abstract     = {Random walk particle tracking (RWPT) is a well established
                      and efficient alternative to grid-based Eulerian approaches
                      when simulating the advection-dispersion transport problem
                      in highly heterogeneous porous media. However, RWPT methods
                      suffer from a lack of accuracy when the dispersion tensor or
                      the water content is spatially discontinuous. We present
                      improvements to the concept of a partially reflecting
                      barrier used to account for these discontinuities : (1) the
                      nonlinear time splitting with root Delta t = root Delta t(1)
                      vertical bar root Delta t(2) that corrects for the
                      systematic overestimation of the second dispersion
                      displacement across an element interface when linear time
                      splitting is used; (2) the one-sided reflection coefficient
                      that correctly represents the effect of discontinuous
                      dispersion coefficients and water content but eliminates
                      redundant reflections of the two-sided reflection
                      coefficient and limits the error for discrete Delta t; and
                      (3) the transformation of the dispersive displacement across
                      the element interface for complex multidimensional transport
                      problems. The proposed improvements are verified numerically
                      by comparison with an analytical solution and a reference
                      RWPT method. The results indicate an increased efficiency
                      and accuracy of the new RWPT algorithm. Because the new
                      algorithm efficiently simulates both advection- and
                      dispersion-dominated transport conditions, it enhances the
                      applicability of RWPT to scenarios in which both conditions
                      occur, as, for example, in the highly transient unsaturated
                      zone. The algorithm is easily implemented and it is shown
                      that the computational benefit increases with increasing
                      variability of the hydraulic parameter field.},
      keywords     = {J (WoSType)},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {Terrestrische Umwelt},
      pid          = {G:(DE-Juel1)FUEK407},
      shelfmark    = {Environmental Sciences / Limnology / Water Resources},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000296339800001},
      doi          = {10.1029/2010WR010267},
      url          = {https://juser.fz-juelich.de/record/17041},
}