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Many minor tweaks, adding self/mass + oxide noshift

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This commit is contained in:
jtclemm
2024-05-14 14:47:11 -06:00
parent da7459c805
commit 343f8afbf6
9 changed files with 100 additions and 26 deletions
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40
doc/src/fix_rheo.rst
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@ -17,7 +17,7 @@ Syntax
* zmin = minimal number of neighbors for reproducing kernels
* zero or more keyword/value pairs may be appended to args
* keyword = *thermal* or *interface/reconstruct* or *surface/detection* or
*shift* or *rho/sum* or *density* or *speed/sound*
*shift* or *rho/sum* or *density* or *self/mass* or *speed/sound*
.. parsed-literal::
@ -29,6 +29,7 @@ Syntax
*limit/splash* = threshold for splash particles
*shift* values = none, turns on velocity shifting
*rho/sum* values = none, uses the kernel to compute the density of particles
*self/mass* values = none, a particle uses its own mass in a rho summation
*density* values = *rho01*, ... *rho0N* (density)
*speed/sound* values = *cs0*, ... *csN* (velocity)
@ -106,24 +107,38 @@ 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.
a kernel summation of the masses of neighboring particles by specifying the *rho/sum*
keyword.
The *density* is used to specify the equilbrium density of each of the N
The *self/mass* keyword modifies the behavior of the density summation in *rho/sum*.
Typically, the density :math:`\rho` of a particle is calculated as the sum
.. math::
\rho_i = \Sum_{j} W_{ij} M_j
where the summation is over neighbors, :math:`W_{ij}` is the kernel, and :math:`M_j`
is the mass of particle :math:`j`. The *self/mass* keyword augments this expression
by replacing :math:`M_j` with :math:`M_i`. This may be useful in simulations of
multiple fluid phases with large differences in density, :ref:`(Hu) <fix_rheo_hu>`.
The *density* keyword is used to specify the equilbrium density of each of the N
particle types. It must be followed by N numerical values specifying each
type's equilibrium density *rho0*.
The *density* is used to specify the speed of sound of each of the N particle
types. It must be followed by N numerical values specifying each type's speed
of sound *cs*.
The *speed/sound* keyword is used to specify the speed of sound of each of the
N particle types. It must be followed by N numerical values specifying each
type's speed of sound *cs*.
Restart, fix_modify, output, run start/stop, minimize info
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
No information about this fix is written to :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
No information about this fix is written to :doc:`binary restart files <restart>`.
None of the :doc:`fix_modify <fix_modify>` options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various :doc:`output commands <Howto_output>`.
No parameter of this fix can be used with the *start/stop* keywords of
the :doc:`run <run>` command. This fix is not invoked during :doc:`energy minimization <minimize>`.
the :doc:`run <run>` command. This fix is not invoked during
:doc:`energy minimization <minimize>`.
Restrictions
""""""""""""
@ -138,7 +153,8 @@ set to all. Only one instance of fix rheo may be defined and it
must be defined prior to all other RHEO fixes.
This fix is part of the RHEO package. It is only enabled if
LAMMPS was built with that package. See the :doc:`Build package <Build_package>` page for more info.
LAMMPS was built with that package. See the
:doc:`Build package <Build_package>` page for more info.
Related commands
""""""""""""""""
@ -156,6 +172,10 @@ Default
----------
.. _howto-howto_rheo_palermo:
.. _howto_rheo_palermo:
**(Palermo)** Palermo, Clemmer, Wolf, O'Connor, in preparation.
.. _fix_rheo_hu:
**(Hu)** Hu, and Adams J. Comp. Physics, 213, 844-861 (2006).

49
doc/src/fix_rheo_viscosity.rst
View File

@ -14,20 +14,26 @@ Syntax
* rheo/viscosity = style name of this fix command
* one or more types and viscosity styles must be appended
* types = lists of types (see below)
* vstyle = *constant*
* vstyle = *constant* or *power*
.. parsed-literal::
*constant* args = *eta*
*eta* = viscosity
*power* args = *eta*, *gd0*, *K*, *n*
*eta* = viscosity
*gd0* = critical strain rate
*K* = consistency index
*n* = power-law exponent
Examples
""""""""
.. code-block:: LAMMPS
fix 1 all rheo/viscosity * constant 1.0
fix 1 all rheo/viscosity 1 constant 1.0 2 constant 2.0
fix 1 all rheo/viscosity 1 constant 1.0 2 power 0.1 5e-4 0.001 0.5
Description
"""""""""""
@ -47,18 +53,38 @@ 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 *types* definition is followed by the viscosity style, *vstyle*. Currently,
the only option is *constant*. Style *constant* simply applies a constant value
of the viscosity *eta* to each particle of the assigned type.
The *types* definition is followed by the viscosity style, *vstyle*. Two
options are available, *constant* and *power*. Style *constant* simply
applies a constant value of the viscosity *eta* to each particle of the
assigned type. Style *power* is a Hershchel-Bulkley constitutive equation
for the stress :math:`\tau`
.. math::
\tau = \left(\frac{\tau_0}{\dot{\gamma}} + K \dot{\gamma}^{n - 1}\right) \dot{\gamma}, \tau \ge \tau_0
where :math:`\dot{\gamma}` is the strain rate and :math:`tau_0` is the critical
yield stress, below which :math:`\dot{\gamma} = 0.0`. To avoid divergences, this
expression is regularized by defining a critical strain rate *gd0*. If the local
strain rate on a particle falls below this limit, a constant viscosity of *eta*
is assigned. This implies a value of
.. math::
\tau_0 = \eta * \dot{\gamma}_0 - K \dot{\gamma}_0^N
as further discussed in :ref:`(Palermo) <howto_rheo_palermo>`.
Restart, fix_modify, output, run start/stop, minimize info
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
No information about this fix is written to :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
No information about this fix is written to :doc:`binary restart files <restart>`.
None of the :doc:`fix_modify <fix_modify>` options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various :doc:`output commands <Howto_output>`.
No parameter of this fix can be used with the *start/stop* keywords of
the :doc:`run <run>` command. This fix is not invoked during :doc:`energy minimization <minimize>`.
the :doc:`run <run>` command. This fix is not invoked during
:doc:`energy minimization <minimize>`.
Restrictions
""""""""""""
@ -69,7 +95,8 @@ conjuction with :doc:`fix rheo <fix_rheo>`. The fix group must be
set to all. Only one instance of fix rheo/viscosity can be defined.
This fix is part of the RHEO package. It is only enabled if
LAMMPS was built with that package. See the :doc:`Build package <Build_package>` page for more info.
LAMMPS was built with that package. See the
:doc:`Build package <Build_package>` page for more info.
Related commands
""""""""""""""""
@ -82,3 +109,9 @@ Default
"""""""
none
----------
.. _howto_rheo_palermo:
**(Palermo)** Palermo, Clemmer, Wolf, O'Connor, in preparation.