User's guide of Proceessing Modflow 5.0

112 Processing Modflow
particle tracking of advective transport in MOC3D. If set to zero, the model will calculate
NPMAX according to eq. 3.31.
NPMAX ' 2 @ NPTPND @ NSROW @ NSCOL @ NSLAY
3.6.2 MOC3D
Fig. 3.35 The Parameters for Advective Transport (MOC3D) dialog box
(3.31)
where NPTPND is the initial number of particles per cell (see below). The values NSROW,
NSCOL and NSLAY are the number of rows, columns and layers of the transport subgrid,
respectively.
< Courant number (CELDIS) is the number of cells (or the fraction of a cell) that a particle
may move through in one step (typically, 0.5 # CELDIS # 1.0).
< Fraction limit for regenerating initial particles (FZERO): If the fraction of active cells
having no particles exceeds FZERO, the program will automatically regenerate an initial
particle distribution before continuing the simulation (typically, 0.01 # FZERO # 0.05).
< Initial number of particles per cell (NPTPND): Valid options for default geometry of
particle placement include 1, 2, 3, or 4 for one-dimensional transport simulation; 1, 4, 9, or
16 for two-dimensional transport simulation; and 1, 8, or 27 for three-dimensional transport
simulation. The user can also customize initial placement of particles by specifying a
negative number to NPTPND, pressing the Tab-key and entering local particle coordinates
into table in the lower part of the dialog box shown in Fig. 3.35, where PNEWL, PNEWR
and PNEWC are relative positions for the initial placement of particles in the layer, row and
column direction, respectively. The local coordinate system range is from -0.5 to 0.5, and
represents the relative distance within the cell about the node location at the center of the
cell, so that the node is located at 0.0 in each direction.