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Documenting new multi-type shifting options

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jtclemm
2024-11-11 15:50:01 -07:00
parent 8521ff0587
commit 9e0047ff06
2 changed files with 58 additions and 17 deletions
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61
doc/src/fix_rheo.rst
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@ -28,9 +28,16 @@ Syntax
values = *sdstyle* *limit* *limit/splash*
*sdstyle* = *coordination* or *divergence*
*limit* = threshold for surface particles
*limit/splash* = threshold for splash particles
*limit/splash* = threshold for splash particles (unitless)
*shift* turns on velocity shifting
values = none
optional args = *exclude/type* or *scale/cross/type*
*exclude/type* values = *types*
*types* = list of types
*scale/cross/type* values = *shiftscale* *cmin* *wmin*
*shiftscale* = fraction of shifting in normal direction to preserve (unitless)
*cmin* = minimum color function value required for scaling (unitless)
*wmin* = minimum local same-type support required for any shifting (unitless)
*rho/sum* density evolution performed by a kernel summation
values = none
optional args = *self/mass*
@ -83,19 +90,49 @@ This is done by estimating the location of the fluid-solid interface and
extrapolating fluid particle properties across the interface to calculate a
temporary apparent density and velocity for a solid particle. The numerical
details are the same as those described in
:ref:`(Palermo) <howto_rheo_palermo>` except there is an additional
:ref:`(Palermo) <fix_rheo_palermo>` except there is an additional
restriction that the reconstructed solid density cannot be less than the
equilibrium density. This prevents fluid particles from sticking to solid
surfaces.
A modified form of Fickian particle shifting can be enabled with the
*shift* keyword. This effectively shifts particle positions to generate a
more uniform spatial distribution. Shifting currently does not consider the
more uniform spatial distribution. By default, shifting does not consider the
type of a particle and therefore may be inappropriate in systems consisting
of multiple fluid phases.
of multiple atom types representing multiple fluid phases. However, two
optional subarguments can follow the *shift* keyword, *exclude/type* and
*scale/cross/type*.
In systems with free surfaces, the *surface/detection* keyword can be used
to classify the location of particles as being within the bulk fluid, on a
The *exclude/type* option lets the user specify a list of atom types which
are not shifted, *types*. A wild-card asterisk can be used in place
of or in conjunction with the *types* argument to set the coefficients for
multiple pairs of atom types. This takes the form "\*" or "\*n" or "m\*"
or "m\*n". If :math:`N` is the number of atom types, then an asterisk with
no numeric values means all types from 1 to :math:`N`. A leading asterisk
means all types from 1 to n (inclusive). A trailing asterisk means all types
from m to :math:`N` (inclusive). A middle asterisk means all types from m to n
(inclusive).
The *scale/cross/type* option is designed to handle interfaces between fluids
made up of different atom types. Similar to the method by
:ref:`(Yang) <fix_rheo_yang>`, a color function is calculated and used to
estimate a local interfacial normal vector. Shifting along this normal direction
is rescaled by a factor of *scaleshift*, such that a value of *scaleshift* of
zero implies there is no shifting in the normal direction and a value of
*scaleshift* of one implies no change in behavior. This scaling is only applied
to atoms with a color function value greater than *cmin*. To handle scenarios
of a small inclusion of one fluid type (e.g. a single atom) inside another,
the amount of same-type support is calculated
.. math::
W_{i,\mathrm{same}} = \sum_{j} W_{ij} \delta_{ij}
where :math:`\delta_{ij}` is zero if atoms :math:`i` and :math:`j` have different
types but unity otherwise. If :math:`W_{i,\mathrm{same}}` is ever less than the
specified value of *wmin*, shifting is turned off for particle :math:`i`
In systems with free surfaces (atom-vacuum), the *surface/detection* keyword
can classify the location of particles as being within the bulk fluid, on a
free surface, or isolated from other particles in a splash or droplet.
Shifting is then disabled in the normal direction away from the free surface
to prevent particles from diffusing away. Surface detection can also be used
@ -117,9 +154,9 @@ threshold for this classification is set by the numerical value of
By default, RHEO integrates particles' densities using a mass diffusion
equation. Alternatively, one can update densities every timestep by performing
a kernel summation of the masses of neighboring particles by specifying the *rho/sum*
keyword. The optional *self/mass* subargument then modifies the behavior of the
density summation. Typically, the density :math:`\rho` of a particle is calculated
as the sum over neighbors
keyword. Following this keyword, one may include the optional *self/mass* subargument
which modifies the behavior of the density summation. Typically, the density
:math:`\rho` of a particle is calculated as the sum over neighbors
.. math::
\rho_i = \sum_{j} W_{ij} M_j
@ -182,6 +219,10 @@ Default
**(Palermo)** Palermo, Wolf, Clemmer, O'Connor, Phys. Fluids, 36, 113337 (2024).
.. _rheo_yang:
**(Yang)** Yang, Rakhsha, Hu, Negrut, J. Comp. Physics, 458, 111079 (2022).
.. _fix_rheo_hu:
**(Hu)** Hu, and Adams J. Comp. Physics, 213, 844-861 (2006).
**(Hu)** Hu, and Adams, J. Comp. Physics, 213, 844-861 (2006).

14
src/RHEO/fix_rheo.cpp
View File

@ -75,7 +75,7 @@ FixRHEO::FixRHEO(LAMMPS *lmp, int narg, char **arg) :
rhosum_self_mass_flag = 0;
shift_cross_type_flag = 0;
int i;
int i, nlo, nhi;
int n = atom->ntypes;
memory->create(rho0, n + 1, "rheo:rho0");
memory->create(csq, n + 1, "rheo:csq");
@ -122,14 +122,14 @@ FixRHEO::FixRHEO(LAMMPS *lmp, int narg, char **arg) :
if (iarg + 3 >= narg) utils::missing_cmd_args(FLERR, "fix rheo shift scale/cross/type", error);
shift_cross_type_flag = 1;
shift_scale = utils::numeric(FLERR, arg[iarg + 1], false, lmp);
shift_wmin = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
shift_cmin = utils::numeric(FLERR, arg[iarg + 3], false, lmp);
shift_cmin = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
shift_wmin = utils::numeric(FLERR, arg[iarg + 3], false, lmp);
iarg += 3;
} else if (strcmp(arg[iarg], "exclude/type") == 0) {
if (iarg + n >= narg) utils::missing_cmd_args(FLERR, "fix rheo shift exclude/type", error);
for (i = 1; i <= n; i++)
shift_type[i] = utils::logical(FLERR, arg[iarg + i], false, lmp);
iarg += n;
if (iarg + 1 >= narg) utils::missing_cmd_args(FLERR, "fix rheo shift exclude/type", error);
utils::bounds(FLERR, arg[iarg + 1], 1, n, nlo, nhi, error);
for (i = nlo; i <= nhi; i++) shift_type[i] = 0;
iarg += 1;
} else {
break;
}